The Armed Forces of the Philippines (AFP) is closely monitoring a mysterious platform spotted inside the lagoon of Bajo de Masinloc (Scarborough or Panatag Shoal) in the West Philippine Sea (WPS) amid concerns that it could become a more permanent structure in the disputed shoal.

AFP Chief Gen. Romeo Brawner Jr. said the military has been conducting aerial surveillance missions over Bajo de Masinloc to determine the nature of the structure.

“We are studying the structure that we spotted. We deployed aircraft over Bajo de Masinloc, or Scarborough Shoal, to determine whether there are structures being built there. We need to establish whether it is a floating structure or a fixed structure,” Brawner said on Monday night, June 8.

The military chief said the latest images taken during a Philippine Air Force (PAF) maritime domain awareness patrol showed the platform remained inside the lagoon.

“At present, it is located in the middle, inside the lagoon itself. It is a six-by-six-meter structure that appears to have an antenna. In the latest image obtained by the Philippine Air Force during a flight over Bajo de Masinloc, there were people on top of it. There were six people on that structure. We do not know what they are doing there,” he said.

The development raised concerns within the national government because of China's previous construction activities in contested areas of the South China Sea, including in Panganiban (Mischief) Reef, Zamora (Subi) Reef, and Kagitingan (Fiery Cross) Reef.

“We will not allow what happened before to happen again. A small structure was built, and later it expanded into an artificial island. We will not allow that to happen at Scarborough Shoal,” Brawner said.

China seized effective control of Bajo de Masinloc after a standoff with the Philippines in 2012. The shoal lies within the Manila’s exclusive economic zone and was among the maritime features covered by the landmark 2016 arbitral ruling that invalidated China's sweeping claims in the South China Sea.

Brawner said the government has already taken diplomatic steps in response to the platform's presence. The Department of Foreign Affairs (DFA) earlier said it issued a diplomatic demarche against China to protest the suspected new feature.

“We are already taking a number of actions. For instance, we have filed a diplomatic protest, and the Department of Foreign Affairs has issued a demarche. We are also in discussions with our allies and partner nations. They are likewise interested in what is happening,” he said.

Meanwhile, the National Task Force for the West Philippine Sea (NTF-WPS) said it was closely coordinating with relevant government agencies to monitor developments and further assess the nature, purpose, and implications of the installation and related activities within the shoal.

It added that inter-agency efforts were underway to establish “a complete and accurate picture of the situation.”

“The protection of Philippine sovereignty, sovereign rights, and jurisdiction remains a paramount consideration,” it said.

The task force reiterated that Bajo de Masinloc “is an integral part of the Philippines and falls within the country's maritime zones as recognized under international law.”

For now, the AFP said surveillance operations will continue.

“Whenever the weather is favorable, we deploy aircraft to monitor what is happening. We will also send ships, including Coast Guard vessels,” Brawner said.