A coordinated surveillance effort by Philippine government agencies enabled authorities to detect and track a Chinese “movable floating platform” inside Bajo de Masinloc (Scarborough or Panatag Shoal) in the West Philippine Sea, revealing a series of developments that have been under daily monitoring since late May.

This was revealed by the National Task Force for the West Philippine Sea (NTF-WPS) in a press conference in Manila on Wednesday, June 10, as it detailed how aerial patrols, satellite imagery and maritime domain awareness (MDA) operations uncovered the platform and other structures in the disputed shoal.

“Government monitoring assets have confirmed the presence of a floating structure within Bajo de Masinloc,” National Security Council Assistant Director-General Cornelio Valencia Jr., co-chair of the NTF-WPS Information Working Group, said during the briefing.

“Relevant agencies continue to gather and validate information regarding its nature, purpose, and activities associated with it. At this stage, I wish to emphasize that monitoring and assessment efforts remain ongoing,” he added.

The platform marks the first such structure documented by the national government in Bajo de Masinloc, and authorities said it was designed to be highly mobile but capable of anchoring firmly into the seabed when needed.

The discovery began with satellite imagery reviewed by the authorities, according to Philippine Coast Guard (PCG) spokesperson for WPS Rear Admiral Jay Tarriela. He said commercial satellite images taken on May 20 showed no man-made structure at the entrance of Bajo de Masinloc, a traditional fishing ground located about 119 nautical miles from Palauig, Zambales.

The shoal lies well within the country’s 200-nautical-mile exclusive economic zone and about 500 nautical miles from Hainan, China’s southernmost province.

The following day, May 21, the PCG documented the presence of two Chinese research vessels near the southeastern entrance of the shoal – Yue Xi Ayu Zhi 20028 and Yue Zhan Yu Ke 6.

“We are suspecting that these two Chinese research vessels are those responsible for bringing the platform into the entrance of Bajo de Masinloc,” Tarriela said.

By May 25, fresh satellite imagery showed a “square object” near the southeast entrance of the shoal. “This was the first indication that there was a structure at the opening of Bajo de Masinloc,” Tarriela said.

The next day, May 26, a routine MDA flight by the Bureau of Fisheries and Aquatic Resources (BFAR) captured the first photograph of the platform and two days later, on May 28, the PCG conducted a low-altitude surveillance flight to obtain a closer look.

The PCG estimated the platform’s deck area at about 30 square meters. The structure measured roughly five meters wide and six to seven meters long. It was surrounded by fenders and equipped with four metal poles believed to be functioning as stilts when the platform is positioned in a fixed location.

“While we were doing an MDA flight (May 28), a PLA (People’s Liberation Army) Navy helicopter also intercepted or tried to harass the Philippine Coast Guard aircraft,” Tarriela bared.

Rather than scaling back surveillance, the PCG said it further intensified monitoring. Tarriela said PCG Commandant Admiral Ronnie Gil Gavan ordered daily MDA flights to document every development around the shoal.

“The intention of Admiral Ronnie Gil Gavan is to document the developments being conducted by the People’s Republic of China since we documented the presence of this movable platform,” he said.

On May 29, authorities again spotted the two Chinese research vessels and detected another buoy in the northern portion of the shoal. A day later, surveillance aircraft photographed six Chinese nationals standing on the movable floating platform and in the same flight, the PCG documented a Chinese rubber boat installing an antenna on a rock formation near the entrance of Bajo de Masinloc.

“We were not just harassed by a PLA Navy helicopter. The Chinese government decided to send a fighter jet to harass and bully the Philippine Coast Guard aircraft while we were conducting this routine MDA flight,” he said.

On May 31, assets from the Armed Forces of the Philippines (AFP), BFAR, and PCG conducted a broader surveillance mission covering the entire shoal. The interagency operation documented four significant developments: an unidentified floating object resembling a container drum, a possible antenna structure near the southern entrance, an additional floating buoy in the north, and the movement of the floating platform from the entrance into the inside of the lagoon.

The PCG also observed two Chinese service boats assisting the transfer of the platform.

“We think there were around 12 to 15 Chinese personnel onboard these service boats and the platform while they were moving it from the opening of Bajo de Masinloc to inside the shoal,” Tarriela said.

Despite the discoveries, the NTF-WPS said it remains cautious about assigning a specific purpose to the platform.

National Maritime Council (NMC) spokesperson Undersecretary Alexander Lopez said the government's assessment so far points to “unlawful and illegal data-gathering activities” by China in Bajo de Masinloc.

“For whatever its purpose, the succeeding actions of the Chinese government will perhaps depend on the information they gather there,” he said.

The presence of the floating platform for possible data-gathering also raised concerns that it could later lead to man-made reclamation of Bajo de Masinloc to a militarized island, similar to what China did to Panganiban (Mischief) Reef, Zamora (Subi) Reef, and Kagitingan (Fiery Cross) Reef.

"If you will notice, we have learned our lessons in the past. The approach of the Chinese Communist Party is salami slicing, or to slowly chip off our territory," said AFP spokesperson for the WPS retired admiral Roy Vincent Trinidad.

"That’s why the pronouncement of our government could be summarized in [not surrendering even] one square inch, and all instruments of the government, including the Department of National Defense, the DOTr [Department of Transportation], the Coast Guard, BFAR, DFA, and all other agencies will ensure that the integrity of the national territory will remain," he added.

For its part, the Department of Foreign Affairs (DFA) said the Philippine government had already lodged diplomatic protests and several demarches against China over the platform and related structures.

“The continued presence of the semi-permanent floating platform, without consent or authorization, is not only a violation of the sovereignty and jurisdiction of the Philippines, but is also inconsistent with international law, particularly UNCLOS [United Nations Convention on the Law of the Sea] and the 2016 South China Sea Arbitral Award,” said DFA spokesperson for maritime affairs Rogelio Villanueva Jr.

For now, the concerned government agencies said they would continue their daily watch over the shoal as Tarriela said the floating platform, antenna, and buoys remain in place while the two Chinese research vessels continue to move in and out of the area.

Further, despite the presence of the structure the PCG and AFP stated that Filipino fishermen can still fish in the vicinity of the shoal and have not reported any recent harassment from the Chinese personnel aboard the new platform.

The NTF-WPS also stated that the national government will not yet seek help from foreign allies for this specific incident, describing the surveillance and response as an internal matter for now.