The China Coast Guard (CCG) ship shadowed the Philippine research vessels BRP H Ventura and the Philippine Coast Guard's BRP Gabriela Silang en route to the Bajo de Masinloc (Scarborough Shoal) in the West Philippine Sea (WPS) on Sunday morning. 

In his X (formerly Twitter) post, maritime security analyst Ray Powell, said "The CCG vessel with bow number 5303 has been tailing the Philippine vessels heading to the Bajo de Masinloc for a hydrographic survey operation."

Powell provided digital imagery showing that the CCG vessel deliberately shadowed the Philippine vessel on a trajectory toward the vicinity of Bajo de Masinloc.

"All 3 ships are now underway en route to the Philippines' survey area north of Scarborough Shoal. China Coast Guard 5303 is shadowing the mission," he said. 

According to Powell, the CCG 5303 blocked the path of the BRP H Ventura and its escort BRP Gabriela Silang about 35 nautical miles from the coast of Luzon which is within the limit of China's nine-dash line in the South China China.

Powell, a former United States Air Force official and ex-Defense Attaché, said the CCG vessel was trying to prevent the Philippine vessels from reaching "their assigned hydrographic research area north of Scarborough Shoal."

The vessels "barely moved" for the past 8 hours on Sunday, he added.

The National Mapping and Resource Information Authority (NAMRIA) earlier issued a maritime advisory that the BRP H Ventura, escorted by BRP Gabriela Silang, will conduct a hydrographic survey north of Bajo de Masinloc (Scarborough Shoal) in the WPS. 

According to NAMRIA, the hydrographic survey involves a systematic field measurement of the depths of various points at sea and the geographic positions of positions of these points.

Powell urged the Philippines, conducting hydrographic surveys in its exclusive economic zone, to be vigilant on possible China's actions against its hydrographic survey mission.