The Philippine Coast Guard (PCG) said it deployed an aircraft on Tuesday, December 30, to challenge a Chinese deep-sea research vessel spotted operating close to the country’s northern coastline, raising fresh concerns over maritime security as tensions escalate around Taiwan.
According to the PCG, the Chinese vessel Tan Suo Er Hao, which serves as a base for submersible and underwater research operations, was detected approximately 19 nautical miles, or about 35 kilometres, off the coast of Cagayan province in northern Luzon. The area lies well within the Philippines’ Exclusive Economic Zone (EEZ), where foreign marine research activities require prior clearance from Manila under both Philippine law and international maritime rules.
The coast guard said a PCG aircraft was dispatched to conduct an aerial challenge after satellite monitoring flagged the presence of the Chinese ship. During the flight, the pilot issued multiple radio calls to the Tan Suo Er Hao, seeking confirmation on whether it was conducting marine scientific research without the consent of the Philippine government.
“Despite repeated radio challenges, no response was received from the Chinese research vessel,” the PCG said in a statement, adding that the silence raised concerns about the nature and intent of the ship’s activities.
The 87.25-metre-long vessel had departed China’s Hainan province earlier this month before entering the western portion of the Philippine EEZ. After being challenged, it was monitored as it continued heading east, later positioning itself about 55.8 nautical miles off Santa Ana town in Cagayan, the PCG said.
Chinese research vessels have long been a sensitive issue in the South China Sea and adjacent waters, with Philippine officials and security analysts warning that some ostensibly civilian ships may also be capable of collecting data with military applications, including seabed mapping and underwater surveillance.
Cagayan’s strategic significance has grown in recent years due to its proximity to Taiwan, which lies just across the Luzon Strait. The province hosts one of nine Philippine military bases accessible to United States forces under the Enhanced Defense Cooperation Agreement (EDCA), a pact that has been expanded as Manila deepens security cooperation with Washington in response to regional security challenges.
The encounter also came against the backdrop of heightened cross-strait tensions. On Tuesday, China conducted large-scale military drills around Taiwan, firing rockets into surrounding waters and simulating strikes and blockades in exercises dubbed “Justice Mission 2025.” The drills were launched just days after the United States announced a record US$11.1 billion arms package for Taipei, a move that Beijing strongly condemned.
While the PCG did not explicitly link the Chinese vessel’s presence off Cagayan to the Taiwan situation, analysts say the timing and location underscore growing anxieties in Manila about being drawn into wider regional tensions.
The PCG said the Tan Suo Er Hao was detected using Canada’s satellite-based Dark Vessel Detection system, which can identify ships even when they are not broadcasting their positions via standard maritime tracking systems. The use of such technology reflects Manila’s efforts to strengthen maritime domain awareness amid increasing activity by foreign vessels in its waters.
The Chinese Embassy in Manila did not immediately respond to a request for comment on the incident. Beijing has previously insisted that its research ships operate in accordance with international law, while the Philippines has repeatedly asserted its sovereign rights within its EEZ.
The latest episode adds to a series of maritime encounters between the Philippines and China over the past year, highlighting the fragile security environment in waters that sit at the crossroads of the South China Sea and the western Pacific.
