China-Philippines Tensions in the South China Sea
link to page 1 
Updated January 23, 2024
China-Philippines Tensions in the South China Sea
Overview
In December 2023, China engaged in what the Philippine
In 2023, the People’s Republic of China (PRC, or China)
government called a “serious escalation” of aggression in
increased pressure on the Philippines to abandon one of its
the South China Sea. PRC vessels reportedly swarmed the
nine outposts in the Spratly Islands chain in the South
area near Second Thomas Shoal and “harassed, blocked,
China Sea (SCS) and attempted to deny Philippine vessels
and executed dangerous maneuvers,” resulting in a collision
access to parts of its Exclusive Economic Zone (EEZ) that
between a PRC coast guard ship and a Philippine boat on a
China claims as its own territory. The escalation of long-
resupply mission. Each side accused the other of ramming
standing Sino-Philippine tensions raises the possibility of a
one of its vessels. Since 2012, the PRC has also harassed
crisis or conflict involving China, the Philippines, and
and blockaded Philippine fishing boats operating near
potentially the United States.
Scarborough Shoal, a traditional fishing area for both
countries (as well as others). In December 2023, the PRC
President Ferdinand Marcos Jr., who was elected in 2022,
Coast Guard deployed a water cannon on Philippine vessels
has taken a considerably more public stance in challenging
attempting to deliver provisions to Filipino fishermen near
China’s expansive claims in the SCS than his predecessor,
the shoal, reportedly damaging the engine of one boat.
Rodrigo Duterte. Marcos has also expanded military
cooperation with the United States under the 2014
Figure 1. South China Sea and Disputed Areas
Enhanced Defense Cooperation Agreement (EDCA), which
aims to support U.S. strategic interests in the region and the
modernization of the Armed Forces of the Philippines.
Rising Tensions at Second Thomas Shoal
Second Thomas Shoal (Tagalog: Ayungin Shoal), an atoll
in the Spratly Island chain, has been a flashpoint among the
broad disputes over sovereignty in the South China Sea
(Figure 1). The Philippines posts a small cadre of its
marines on a now-derelict Philippine Navy ship, the Sierra
Madre, which it grounded on the shoal in 1999 as part of its
efforts to protect its maritime claims. Since 2013, China has
increased its presence near the shoal as part of its attempt to
end the Philippines’ occupation there. Second Thomas
Shoal is a low-tide elevation (meaning it is fully submerged
at high tide) located roughly 105 nautical miles (nm) from
the Philippine island of Palawan, 620 nm from the PRC,
and 22 nm from Mischief Reef, a low-tide elevation in the
Spratlys where the PRC maintains an outpost. The PRC
government claims that Joseph Estrada (president of the
Philippines from 1998-2001) promised to remove the Sierra
Source: CRS. Boundaries from U.S. Department of State.
Madre, which the Marcos government denies.
In 2023, PRC Coast Guard and maritime militia vessels
A spokesperson for the China Coast Guard stated its
interfered with Philippine boats conducting resupply
December 2023 actions were “professional, standardized,
missions to the Sierra Madre. Among the most notable
legitimate, and legal.” Despite PRC efforts, the Philippines
incidents, in February 2023, a PRC coast guard vessel
reportedly successfully resupplied the Sierra Madre on
targeted a Philippine coast guard boat with a military-grade
several occasions in 2023, and airdropped some supplies in
laser, reportedly temporarily blinding some crew members.
January 2024. The U.S. State Department has issued
In August, PRC coast guard and maritime militia vessels
multiple statements critical of PRC actions and supportive
fired a water cannon and took other actions to obstruct
of the Philippines’ right to operate in waters around Second
Philippine boats near the shoal. In October, PRC coast
Thomas Shoal. On October 22, 2023, the State Department
guard and maritime militia vessels surrounded and collided
reaffirmed U.S. obligations to the Philippines pursuant to
with a Philippine coast guard vessel and another supply
the two countries’ 1951 Mutual Defense Treaty.
vessel. The incident reportedly was the first time Philippine
officials stated their vessels were struck by PRC ships.
President Marcos assumed office pledging to defend the
country’s sovereign rights, but also to work with China. In
January 2023, during a visit to Beijing, he and PRC leader
Xi Jinping announced a hotline to manage tensions and
https://crsreports.congress.gov
China-Philippines Tensions in the South China Sea
prevent escalations. Efforts to use the mechanism to
training to the Philippines” between 2015 and 2022, making
manage the August incidents went unanswered in Beijing,
it the “largest recipient of U.S. military assistance in the
however. Following the incidents in December 2023,
Indo-Pacific region.” Enhancing the Philippines’ maritime
Marcos vowed to step up the Philippines defense of its
security capabilities has been a key focus of that assistance.
maritime zones.
Under EDCA, the two countries agreed to deepen military
cooperation and allow U.S. forces rotational access to
SCS Territorial Disputes and International Law
certain Philippine military facilities. In 2023, the number of
An arbitral tribunal convened under the United Nations
these bases expanded from five to nine. The United States
Convention on the Law of the Sea (UNCLOS) ruled in
and the Philippines engage in approximately 20 military
2016 that the “Nine-Dash Line,” which China uses to mark
exercises and events annually, including patrols in the SCS.
its territorial claims in the SCS, has “no legal basis,” and
that several PRC actions in the SCS violated the
Considerations for Congress
Philippines’ sovereign rights. The tribunal found that
U.S. options to support Philippine efforts to defend its
Second Thomas Shoal and the PRC-occupied Mischief
sovereign rights within its EEZ include U.S. military, quasi-
Reef, as well as Scarborough Shoal, fall within the
military, and diplomatic actions. Congress may consider
Philippines’ EEZ, and that China had unlawfully interfered
whether or not to support or promote such efforts. On
with Philippine fishing at Scarborough Shoal and created a
October 25, three U.S. Senators submitted a letter to
risk of collision. China declared the ruling “null and void.”
President Biden requesting the departments of State and
(For more on the disputes, see CRS In Focus IF10607,
Defense provide “a full list” of options to “support the
China Primer: South China Sea Disputes.)
Philippines and ensure the resupply” of the Sierra Madre.
The government of the United States, which is not a party
Military options could include sending a rotation of U.S.
to UNCLOS, has urged both Beijing and Manila to abide by
forces to support Philippine troops on the Sierra Madre or
the 2016 ruling. The State Department noted in a December
U.S. Navy escorts to Philippine defensive missions. Some
10, 2023 statement that China’s actions were not in line
observers caution that a direct U.S. military role supporting
with international law:
the Philippines could increase the risk of an incident
between U.S. and PRC forces. Some recommend less-direct
These actions reflect not only reckless disregard for
forms of U.S. support, such as providing additional military
the safety and livelihoods of Filipinos, but also for
assistance and training to the Philippines; expanding U.S.
international law. As reflected in an international
force posture in the region; coordinating with other
tribunal’s legally binding decision issued in July
claimants to counter PRC territorial ambitions; and keeping
2016, the PRC has no lawful maritime claims to the
U.S. lines of communication open with Beijing.
waters around Second Thomas Shoal, and Filipinos
are entitled to traditional fishing rights around
Non-military options could involve the U.S. Coast Guard
Scarborough Reef. As provided under the 1982
(USCG). In September 2023 testimony to the House
Committee on Homeland Security Subcommittee on
Law of the Sea Convention, the 2016 arbitral
Transportation and Maritime Security, the commander of
decision is final and legally binding on the PRC and
USCG Pacific Area touted the USCG’s “outstanding
the Philippines, and the United States calls upon the
relationship” with the Philippine Coast Guard and ongoing
PRC to abide by the ruling and desist from its
efforts to help the Philippines “enforce their sovereignty.”
dangerous and destabilizing conduct.
The USCG’s FY2024 Unfunded Priorities List includes
U.S.-Philippines Mutual Defense Treaty
$400,000 for the acquisition of four new vessels to help
“the Coast Guard transition … from an organization which
Under Article IV of their Mutual Defense Treaty, the
United States and the Philippines recognize that “an armed
currently provides episodic presence [in the Indo-Pacific],
to be persistent and visible, strengthening coordination with
attack in the Pacific Area on either of the Parties would be
Allied and partner nations to bolster regional security.”
dangerous to its own peace and safety and declares that it
would act to meet the common dangers in accordance with
its constitutional processes.” Article V defines such an
Congress may also consider how U.S. accession to
armed attack as including an attack on the “metropolitan
UNCLOS would impact U.S. diplomacy. The United States
accepts and acts in accordance with UNCLOS’s provisions
territory of either of the Parties, or on the island territories
on navigation and overflight, which it views as reflecting
under its jurisdiction in the Pacific or on its armed forces,
public vessels or aircraft in the Pacific.” The Treaty does
customary international law of the sea. Some analysts argue
U.S. accession to UNCLOS would strengthen U.S. calls for
not specifically refer to the SCS. New Bilateral Defense
other countries to abide by the Convention’s provisions and
Guidelines, issued in May 2023, appear to reinforce treaty
the 2016 arbitral ruling, which is largely in the Philippines’
obligations, stating that an armed attack “anywhere in the
South China Sea,” on either country’s “public vessels,
favor. (For background on this debate, see “Whether United
States Should Ratify UNCLOS,” in CRS Report R42784,
aircraft, or armed forces—which includes their Coast
U.S.-China Strategic Competition in South and East China
Guards—would invoke mutual defense commitments.”
Seas: Background and Issues for Congress.)
U.S.-Philippines Security Cooperation
According to the U.S. Embassy in Manila, the United States
Caitlin Campbell, Analyst in Asian Affairs
“delivered [over $1.14 billion] worth of planes, armored
Ben Dolven, Specialist in Asian Affairs
vehicles, small arms, and other military equipment and
Thomas Lum, Specialist in Asian Affairs
https://crsreports.congress.gov
China-Philippines Tensions in the South China Sea
IF12550
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF12550 · VERSION 3 · UPDATED
Updated January 23, 2024
China-Philippines Tensions in the South China Sea
Overview
In December 2023, China engaged in what the Philippine
In 2023, the People’s Republic of China (PRC, or China)
government called a “serious escalation” of aggression in
increased pressure on the Philippines to abandon one of its
the South China Sea. PRC vessels reportedly swarmed the
nine outposts in the Spratly Islands chain in the South
area near Second Thomas Shoal and “harassed, blocked,
China Sea (SCS) and attempted to deny Philippine vessels
and executed dangerous maneuvers,” resulting in a collision
access to parts of its Exclusive Economic Zone (EEZ) that
between a PRC coast guard ship and a Philippine boat on a
China claims as its own territory. The escalation of long-
resupply mission. Each side accused the other of ramming
standing Sino-Philippine tensions raises the possibility of a
one of its vessels. Since 2012, the PRC has also harassed
crisis or conflict involving China, the Philippines, and
and blockaded Philippine fishing boats operating near
potentially the United States.
Scarborough Shoal, a traditional fishing area for both
countries (as well as others). In December 2023, the PRC
President Ferdinand Marcos Jr., who was elected in 2022,
Coast Guard deployed a water cannon on Philippine vessels
has taken a considerably more public stance in challenging
attempting to deliver provisions to Filipino fishermen near
China’s expansive claims in the SCS than his predecessor,
the shoal, reportedly damaging the engine of one boat.
Rodrigo Duterte. Marcos has also expanded military
cooperation with the United States under the 2014
Figure 1. South China Sea and Disputed Areas
Enhanced Defense Cooperation Agreement (EDCA), which
aims to support U.S. strategic interests in the region and the
modernization of the Armed Forces of the Philippines.
Rising Tensions at Second Thomas Shoal
Second Thomas Shoal (Tagalog: Ayungin Shoal), an atoll
in the Spratly Island chain, has been a flashpoint among the
broad disputes over sovereignty in the South China Sea
(Figure 1). The Philippines posts a small cadre of its
marines on a now-derelict Philippine Navy ship, the Sierra
Madre, which it grounded on the shoal in 1999 as part of its
efforts to protect its maritime claims. Since 2013, China has
increased its presence near the shoal as part of its attempt to
end the Philippines’ occupation there. Second Thomas
Shoal is a low-tide elevation (meaning it is fully submerged
at high tide) located roughly 105 nautical miles (nm) from
the Philippine island of Palawan, 620 nm from the PRC,
and 22 nm from Mischief Reef, a low-tide elevation in the
Spratlys where the PRC maintains an outpost. The PRC
government claims that Joseph Estrada (president of the
Philippines from 1998-2001) promised to remove the Sierra
Source: CRS. Boundaries from U.S. Department of State.
Madre, which the Marcos government denies.
In 2023, PRC Coast Guard and maritime militia vessels
A spokesperson for the China Coast Guard stated its
interfered with Philippine boats conducting resupply
December 2023 actions were “professional, standardized,
missions to the Sierra Madre. Among the most notable
legitimate, and legal.” Despite PRC efforts, the Philippines
incidents, in February 2023, a PRC coast guard vessel
reportedly successfully resupplied the Sierra Madre on
targeted a Philippine coast guard boat with a military-grade
several occasions in 2023, and airdropped some supplies in
laser, reportedly temporarily blinding some crew members.
January 2024. The U.S. State Department has issued
In August, PRC coast guard and maritime militia vessels
multiple statements critical of PRC actions and supportive
fired a water cannon and took other actions to obstruct
of the Philippines’ right to operate in waters around Second
Philippine boats near the shoal. In October, PRC coast
Thomas Shoal. On October 22, 2023, the State Department
guard and maritime militia vessels surrounded and collided
reaffirmed U.S. obligations to the Philippines pursuant to
with a Philippine coast guard vessel and another supply
the two countries’ 1951 Mutual Defense Treaty.
vessel. The incident reportedly was the first time Philippine
officials stated their vessels were struck by PRC ships.
President Marcos assumed office pledging to defend the
country’s sovereign rights, but also to work with China. In
January 2023, during a visit to Beijing, he and PRC leader
Xi Jinping announced a hotline to manage tensions and
https://crsreports.congress.gov
China-Philippines Tensions in the South China Sea
prevent escalations. Efforts to use the mechanism to
training to the Philippines” between 2015 and 2022, making
manage the August incidents went unanswered in Beijing,
it the “largest recipient of U.S. military assistance in the
however. Following the incidents in December 2023,
Indo-Pacific region.” Enhancing the Philippines’ maritime
Marcos vowed to step up the Philippines defense of its
security capabilities has been a key focus of that assistance.
maritime zones.
Under EDCA, the two countries agreed to deepen military
cooperation and allow U.S. forces rotational access to
SCS Territorial Disputes and International Law
certain Philippine military facilities. In 2023, the number of
An arbitral tribunal convened under the United Nations
these bases expanded from five to nine. The United States
Convention on the Law of the Sea (UNCLOS) ruled in
and the Philippines engage in approximately 20 military
2016 that the “Nine-Dash Line,” which China uses to mark
exercises and events annually, including patrols in the SCS.
its territorial claims in the SCS, has “no legal basis,” and
that several PRC actions in the SCS violated the
Considerations for Congress
Philippines’ sovereign rights. The tribunal found that
U.S. options to support Philippine efforts to defend its
Second Thomas Shoal and the PRC-occupied Mischief
sovereign rights within its EEZ include U.S. military, quasi-
Reef, as well as Scarborough Shoal, fall within the
military, and diplomatic actions. Congress may consider
Philippines’ EEZ, and that China had unlawfully interfered
whether or not to support or promote such efforts. On
with Philippine fishing at Scarborough Shoal and created a
October 25, three U.S. Senators submitted a letter to
risk of collision. China declared the ruling “null and void.”
President Biden requesting the departments of State and
(For more on the disputes, see CRS In Focus IF10607,
Defense provide “a full list” of options to “support the
China Primer: South China Sea Disputes.)
Philippines and ensure the resupply” of the Sierra Madre.
The government of the United States, which is not a party
Military options could include sending a rotation of U.S.
to UNCLOS, has urged both Beijing and Manila to abide by
forces to support Philippine troops on the Sierra Madre or
the 2016 ruling. The State Department noted in a December
U.S. Navy escorts to Philippine defensive missions. Some
10, 2023 statement that China’s actions were not in line
observers caution that a direct U.S. military role supporting
with international law:
the Philippines could increase the risk of an incident
between U.S. and PRC forces. Some recommend less-direct
These actions reflect not only reckless disregard for
forms of U.S. support, such as providing additional military
the safety and livelihoods of Filipinos, but also for
assistance and training to the Philippines; expanding U.S.
international law. As reflected in an international
force posture in the region; coordinating with other
tribunal’s legally binding decision issued in July
claimants to counter PRC territorial ambitions; and keeping
2016, the PRC has no lawful maritime claims to the
U.S. lines of communication open with Beijing.
waters around Second Thomas Shoal, and Filipinos
are entitled to traditional fishing rights around
Non-military options could involve the U.S. Coast Guard
Scarborough Reef. As provided under the 1982
(USCG). In September 2023 testimony to the House
Committee on Homeland Security Subcommittee on
Law of the Sea Convention, the 2016 arbitral
Transportation and Maritime Security, the commander of
decision is final and legally binding on the PRC and
USCG Pacific Area touted the USCG’s “outstanding
the Philippines, and the United States calls upon the
relationship” with the Philippine Coast Guard and ongoing
PRC to abide by the ruling and desist from its
efforts to help the Philippines “enforce their sovereignty.”
dangerous and destabilizing conduct.
The USCG’s FY2024 Unfunded Priorities List includes
U.S.-Philippines Mutual Defense Treaty
$400,000 for the acquisition of four new vessels to help
“the Coast Guard transition … from an organization which
Under Article IV of their Mutual Defense Treaty, the
United States and the Philippines recognize that “an armed
currently provides episodic presence [in the Indo-Pacific],
to be persistent and visible, strengthening coordination with
attack in the Pacific Area on either of the Parties would be
Allied and partner nations to bolster regional security.”
dangerous to its own peace and safety and declares that it
would act to meet the common dangers in accordance with
its constitutional processes.” Article V defines such an
Congress may also consider how U.S. accession to
armed attack as including an attack on the “metropolitan
UNCLOS would impact U.S. diplomacy. The United States
accepts and acts in accordance with UNCLOS’s provisions
territory of either of the Parties, or on the island territories
on navigation and overflight, which it views as reflecting
under its jurisdiction in the Pacific or on its armed forces,
public vessels or aircraft in the Pacific.” The Treaty does
customary international law of the sea. Some analysts argue
U.S. accession to UNCLOS would strengthen U.S. calls for
not specifically refer to the SCS. New Bilateral Defense
other countries to abide by the Convention’s provisions and
Guidelines, issued in May 2023, appear to reinforce treaty
the 2016 arbitral ruling, which is largely in the Philippines’
obligations, stating that an armed attack “anywhere in the
South China Sea,” on either country’s “public vessels,
favor. (For background on this debate, see “Whether United
States Should Ratify UNCLOS,” in CRS Report R42784,
aircraft, or armed forces—which includes their Coast
U.S.-China Strategic Competition in South and East China
Guards—would invoke mutual defense commitments.”
Seas: Background and Issues for Congress.)
U.S.-Philippines Security Cooperation
According to the U.S. Embassy in Manila, the United States
Caitlin Campbell, Analyst in Asian Affairs
“delivered [over $1.14 billion] worth of planes, armored
Ben Dolven, Specialist in Asian Affairs
vehicles, small arms, and other military equipment and
Thomas Lum, Specialist in Asian Affairs
https://crsreports.congress.gov
China-Philippines Tensions in the South China Sea
IF12550
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF12550 · VERSION 3 · UPDATED