Two Chinese research vessels were spotted operating within the Philippines’ exclusive economic zone (EEZ), the Philippine Coast Guard (PCG) reported on Tuesday.

The vessels were identified as Xiang Yang Hong 302 and Tan Suo Er Hao.

At a press conference in Manila, PCG spokesperson for the West Philippine Sea Commodore Jay Tarriela said Xiang Yang Hong 302 departed from Hainan, China, on 1 May and was detected 180 nautical miles off the coast of Rizal, Palawan, at around 8:00 AM on Tuesday, 20 May.

Tarriela said Xiang Yang Hong 302 is 100 meters long, weighs 4,500 tons, and is capable of conducting deep-sea surveys.

"This is the reason why it is also equipped with remotely operated vehicles and private underwater drones,” he said.

He added that the vessel operates under China’s State Oceanic Administration and is intended for use by the People’s Liberation Army Navy for oceanographic research.

Meanwhile, Tan Suo Er Hao departed Hainan on 8 May and was located 130.5 nautical miles from Burgos, Ilocos Norte.

Tarriela noted that Tan Suo Er Hao has similar capabilities to Xiang Yang Hong 302, including deep-sea research functions.

“This Chinese research vessel is under the administration of China Ocean Mineral Resources Research and Development Association (COMRA), and it is manned by the Institute of Deep-sea Science and Engineering,” he said.

To monitor the vessel’s activity, the PCG deployed an aircraft for a maritime domain awareness flight over Tan Suo Er Hao.

In addition to the two vessels, Tarriela confirmed that Zhong Shan Da Xue was also detected within the Philippine EEZ but departed and returned to Guangdong at 9:56 AM on 20 May. The vessel, owned by Sun Yat-sen University, had been operating since 31 March.

"It spent a considerable large number of conducting marine scientific research up north within the EEZ of the Philippines and sometimes crossing also the Taiwan Strait. It only returned to Guangdong province on 20 May," Tarriela said.

He stressed that the navigation patterns show the vessel was conducting marine scientific research in Philippine waters.

“As you can see from the navigation pattern of this Chinese research vessel, the Chinese government cannot deny that what they are doing there is actually marine scientific research,” he said. “Probably, the Chinese government can also reason that it is purely for scientific and civilian use."

Tarriela further mentioned that findings from the research vessel are believed to be shared with the People’s Liberation Army Navy.

"The scientific findings of this research vessel is also being forwarded to the PLA Navy for whatever reasons that they can make use of those data,” he added.