MANILA— The Philippine Coast Guard (PCG) has deployed aircraft and vessels to monitor and challenge a Chinese deep-sea research ship operating near Hubo Reef in the West Philippine Sea, saying the vessel was conducting marine scientific research within the country’s exclusive economic zone (EEZ) without authorization.

The deployment was ordered by PCG Commandant Admiral Ronnie Gil Gavan after a maritime surveillance flight on Oct. 11 tracked the Chinese vessel TAN SUO YI HAO near Hubo Reef, also known as Hardy Reef.

The Department of Foreign Affairs (DFA) confirmed that China had not requested Philippine consent for the vessel to conduct marine scientific research in the country’s EEZ, according to the PCG.

Using Dark Vessel Detection and automatic identification system (AIS) tracking, the PCG determined that the research ship left the vicinity of Sanya, Hainan, on Oct. 2 and entered the Philippine EEZ at 7:30 p.m. on Oct. 9 after transiting the western side of the South China Sea.

On the morning of Oct. 10, the vessel was stationary approximately 12 nautical miles northwest of Katimugan Bank. It declared through its AIS that it was conducting diving operations and had restricted maneuverability, while instructing other vessels to keep a distance of two nautical miles.

The ship also indicated an estimated arrival date of Oct. 17, suggesting it intended to remain in the area for at least another week.

The vessel subsequently stopped transmitting its AIS signal before resuming transmission. As of 1:45 p.m. on Oct. 11, it was underway approximately 5.63 nautical miles west-northwest of Hubo Reef and 116.72 nautical miles northwest of Rizal, Palawan, while continuing to declare diving operations and restricted maneuverability.

During a maritime domain awareness flight launched from Antonio Bautista Air Base in Puerto Princesa City on Oct. 11, a PCG Islander aircraft spotted the Chinese vessel at 8:13 a.m., approximately five nautical miles west-northwest of Hubo Reef, moving slowly eastward.

The PCG said its aircrew observed no deployed submersible, equipment or lines in the water during the overflight. The aircraft issued several radio challenges to the research vessel, but received no response.

The same flight monitored China Coast Guard vessel CCG 5306 approximately 6.8 nautical miles south of Hubo Reef and another Chinese coast guard vessel about 12.7 nautical miles southwest of the reef.

Two People’s Liberation Army Navy vessels were also spotted in nearby waters, one approximately 22.8 nautical miles northeast of Escoda Shoal and the other about 11.3 nautical miles south-southeast of Katimugan Bank.

The PCG identified TAN SUO YI HAO as a vessel operated by the Institute of Deep-sea Science and Engineering of the Chinese Academy of Sciences, based in Sanya. It serves as a mothership for China’s deep-sea manned submersibles, including Fendouzhe, and is equipped with deep-sea winches, sounding systems and sediment collection devices used for seabed investigations.

According to the PCG, the vessel is the first among the Chinese research ships it recently monitored to openly declare diving operations within the Philippine EEZ. It is also operating farther into the southern portion of the West Philippine Sea than the other research vessels monitored.

Gavan said the presence of the research ship formed part of a broader pattern of Chinese fishing and research activities across Philippine waters.

“These are not isolated incidents. China is orchestrating the use of fishing vessels and marine scientific research vessels in multiple areas of our maritime domain to thinly spread our operational capabilities, strain our logistics and sustainment, and pressure the Philippines toward acquiescence to a normalized, illegal, and expansive claim. The PCG will not waver. We will execute the guidance of the President not to lose even a square inch of our territory and jurisdiction,” Gavan said.

The PCG cited several other recent incidents involving Chinese vessels, including the operation of research vessel JIA HAI KE 7 northwest of Itbayat, Batanes, and the presence of Chinese Maritime Militia Vessel 9622 and 22 sampans conducting unauthorized fishing within the territorial sea of Kota Island in the Kalayaan Island Group. The PCG said it repelled the fishing vessels on Oct. 9.

Before these incidents, Chinese survey vessel HAIYANG DIZHI SHIHAO had loitered off Bajo de Masinloc for nearly a month, the agency added.

The PCG said the Philippines exercises sovereign rights and jurisdiction over its EEZ and continental shelf under Articles 56, 77 and 246 of the 1982 United Nations Convention on the Law of the Sea (UNCLOS). Marine scientific research in these areas requires the consent of the Philippine government, it said.

These rights were affirmed by the 2016 Arbitral Award and further codified in the Philippine Maritime Zones Act, according to the agency. It maintained that any seabed survey, sampling or mapping conducted by TAN SUO YI HAO without Philippine consent would be unauthorized.

The PCG said it would continue monitoring the vessel and coordinate with the National Task Force for the West Philippine Sea and the DFA for appropriate action.

The deployment follows President Ferdinand R. Marcos Jr.’s position that the Philippines would not relinquish any part of its territory to a foreign power. On Oct. 8, the President reiterated that international law, particularly UNCLOS, recognizes the areas in question as part of Philippine sovereign territory and its exclusive economic zone.