A Chinese research vessel openly declared for the first time its diving operation inside Philippine waters in the West Philippine Sea, the Philippine Coast Guard (PCG) said Monday.

The PCG reported that Tan Suo Yi Haoi is conducting unauthorized operations inside the Philippine Exclusive Economic Zone (EEZ) in the vicinity of Hubo Reef (Hardy Reef).

"It is the first among the Chinese research vessels recently monitored by the PCG to openly declare diving operations inside the Philippine EEZ, and the one operating farthest into the southern portion of the West Philippine Sea," it said.

The Department of Foreign Affairs (DFA) confirmed that no request for consent was received from China for any marine scientific research to be conducted by Tan Suo Yi Hao.

Tan Suo Yi Hao. which is operated by the Institute of Deep-sea Science and Engineering of the Chinese Academy of Sciences based in Sanya ,serves as a mother ship for China's manned submersibles and is equipped with deep-sea winches, sounding systems, and sediment collection devices for seabed investigation.

Through Dark Vessel Detection (DVD) and AIS (Automatic Identification System) tracking, the PCG established that the Chinese research vessel departed the vicinity of Sanya, Hainan on October 2, transited the western side of the South China Sea, and entered the Philippine EEZ at 7:30 pm on October 9.

On the morning of October 10, it was lying-to approximately 12 nautical miles northwest of Katimugan Bank, and declared through its AIS that it was engaged in diving operations with restricted maneuverability, while directing other vessels to keep two nautical miles clear.

The PCG noted that the Chinese research vessel "also declared an estimated time of arrival of October 17, indicating its intent to remain in the area for at least another week."

"The vessel subsequently went silent on AIS before resuming transmission. As of 1:45 PM on 11 October 2026, Tan Suo Yi Hao was underway approximately 5.63 nautical miles west-northwest of Hubo Reef and 116.72 nautical miles northwest of Rizal, Palawan, still declaring restricted maneuverability and diving operations," it stated.

Upon the directive of PCG Commandant Admiral Ronnie Gil Gavan, it deployed aircraft and vessels to challenge and disrupt the illegal marine scientific research of the Chinese research vessel.

On Sunday morning, a PCG Islander aircraft conducted a Maritime Domain Awareness (MDA) flight from Antonio Bautista Air Base in Puerto Princesa City and located the Chinese ship approximately five nautical miles west-northwest of Hubo Reef, slowly navigating eastward.

"No deployed submersible, equipment, or lines were observed in the water at the time of the overflight. The PCG aircraft issued multiple radio challenges to the Chinese research vessel, all of which went unanswered," said PCG.

During the same flight, the China Coast Guard vessel CCG 5306 was also monitored approximately 6.8 nautical miles south of Hubo Reef, and another China Coast Guard vessel was also spotted approximately 12.7 nautical miles southwest of Hubo Reef.

"Two People's Liberation Army Navy vessels were likewise monitored in the surrounding waters, one approximately 22.8 nautical miles northeast of Escoda Shoal and the other approximately 11.3 nautical miles south-southeast of Katimugan Bank, "it stated.

Following the results of the MDA flight, Gavan ordered the deployment of PCG vessels to directly challenge the Chinese ship and disrupt its illegal activities within the Philippine EEZ.

Gavan said the presence of Tan Suo Yi Hao is "not an isolated incident" noting that in recent weeks, the PCG has responded to Chinese research vessel Jia Hai Ke 7 operating northwest of Itbayat, Batanes, and to Chinese Maritime Militia Vessel 9622 and its 22 sampans conducting unauthorized fishing within the territorial sea of Kota Island in the Kalayaan Island Group, which the PCG repelled on October 9.

Prior to these, Chinese survey vessel Haiyang Dizhi Shihao loitered off Bajo de Masinloc for nearly a month.

"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," said Gavan.

"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," he added. Robina Asido/PHS