The Philippine Coast Guard deployed an aircraft on 30 December to challenge a Chinese deep sea research vessel detected inside the country’s exclusive economic zone off the northern province of Cagayan, an area close to Taiwan.
The vessel, identified as the CRV Tan Suo Er Hao, was first spotted around 19 nautical miles from the coast of Cagayan province using Canada’s satellite based Dark Vessel Detection system. Philippine authorities later tracked the ship approximately 55.8 nautical miles off Santa Ana, Cagayan.
The 87.25 metre vessel is operated by the Institute of Deep sea Science and Engineering under the Chinese Academy of Sciences. It functions as a mother ship for manned and unmanned submersibles and supports advanced deep sea exploration missions.
According to the Philippine Coast Guard, its pilot issued multiple radio challenges to the vessel to determine whether it was conducting marine scientific research without authorisation from Manila. Such activity would violate both Philippine and international law. The challenges received no response.
Monitoring data showed the vessel had departed from Hainan province in China earlier in December. It entered the western portion of the Philippine exclusive economic zone before heading east toward waters off northern Luzon.
Cagayan, the northernmost province of Luzon, holds strategic significance due to its proximity to Taiwan. The province hosts key military facilities, including locations accessible to United States forces under the Enhanced Defense Cooperation Agreement.
The Chinese embassy in Manila said the vessel was conducting what it described as normal manoeuvres. It added that China does not recognise certain Philippine domestic maritime laws and maintains that, under international law, it has the right to pass through the waters as part of a maritime route.
The incident took place amid heightened regional tensions. On 30 December, China conducted large scale military exercises around Taiwan under the name Justice Mission 2025. The drills involved troops, warships, fighter jets and artillery, including live fire exercises, simulated strikes on land and sea targets, and rehearsals to blockade key ports.
The exercises followed a United States announcement earlier in December approving a record $11.1 billion arms package for Taiwan, which includes advanced rocket systems, howitzers and drones.
Philippine Defence Secretary Gilberto Teodoro said Manila was deeply concerned by China’s military and coast guard actions around Taiwan, warning of broader regional implications.
“This heightened scale of coercion has implications that extend beyond cross Strait relations and into the broader Indo Pacific community,” he said in a statement issued on Wednesday.
The Philippines has repeatedly asserted its sovereign rights within its exclusive economic zone under the United Nations Convention on the Law of the Sea, as well as the 2016 arbitral ruling that invalidated expansive Chinese claims in the South China Sea.
Throughout 2025, the Philippine Coast Guard said it had monitored more than two dozen Chinese research vessels entering the country’s exclusive economic zone, underscoring ongoing maritime tensions in waters near strategically sensitive areas.
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