The Philippine Coast Guard (PCG) said it drove away a Chinese research vessel that had been allegedly conducting “unauthorized” marine scientific research (MSR) near cays within the territorial sea of Pag-asa (Thitu) Island in the West Philippine Sea (WPS).

In a statement on Sunday night, May 17, PCG spokesperson for WPS Rear Adm. Jay Tarriela said the coast guard carried out a maritime domain awareness (MDA) flight on Sunday, May 17, after Chinese personnel were seen landing on Sandy Cay 2 and later moving to Sandy Cay 3.

The MDA flight used PCG Islander 4177 to monitor the waters around Sandy Cay 2 and Sandy Cay 3 and during the patrol, the aircraft spotted Xiang Yang Hong 33, a China-flagged research ship capable of deep-sea surveys, bathymetric mapping, and marine ecological studies; as well as 20 Chinese maritime militia vessels scattered near Sandy Cay 3 and Sandy Cay 4.

The research vessel was escorted by two China Coast Guard (CCG) ships with bow numbers “5101” and “5309”. The PCG said the Chinese ships deployed rigid-hulled inflatable boats and rubber boats during the operation.

“Chinese personnel were observed landing and conducting illegal activities on Cay 2 before proceeding to Cay 3,” Tarriela said.

The cays are near Pag-asa Island, which the Philippines occupies as part of the Kalayaan Island Group (KIG) in the Spratly chain. The area has become a recurring flashpoint between Manila and Beijing amid competing claims in the South China Sea.

The PCG said its aircraft issued several radio challenges to the Chinese vessels and ordered them to stop their activities.

According to the PCG, Xiang Yang Hong 33 left Guangzhou on April 15 and entered WPS on April 18. It said the vessel had spent nearly a month conducting “illegal” marine scientific research across Philippine waters.

Under the United Nations Convention on the Law of the Sea (UNCLOS), foreign states must secure consent from a coastal state before conducting marine scientific research inside its territorial sea.

“The PCG emphasizes that these activities constitute unauthorized Marine Scientific Research within the Philippines’ territorial sea, in clear violation of Philippine sovereignty and the United Nations Convention on the Law of the Sea (UNCLOS),” Tarriela said.

The national government has repeatedly protested the presence of Chinese maritime militia and coast guard ships near Philippine-held features in the WPS.

Tensions have intensified in recent years after a series of confrontations near critical features including Ayungin Shoal, Bajo de Masinloc, and Pag-asa Island.

“The PCG remains steadfast in defending our maritime zones. We will not allow any unauthorized foreign research or incursions into our territorial sea in Pag-asa Island in accordnace with the directive of President Ferdinand Marcos, Jr.,” said PCG Commandant Admiral Ronnie Gil Gavan.

“Our presence and patrols in the West Philippine Sea are consistent, lawful, and resolute,” he added.