A National Security Council (NSC) official warned any attempt by China to construct and turn Scarborough Shoal into an island would cross a "red line" for the Philippines, potentially triggering regional instability.

Speaking at a virtual forum organized by the Stratbase ADR Institute on Tuesday, NSC Assistant Director General and spokesperson Jonathan Malaya revealed that Philippine authorities have observed a significant increase in the presence and activities of Chinese coast guard and suspected militia vessels at the shoal in recent years, fueling speculation about Beijing’s intentions in the contested area.

He cited the country’s current policy of not yielding even an inch of Philippine territory to China in the West Philippine Sea (WPS) as the basis for declaring the red line.

“What keeps us awake at night is that China, since they have presence in the area, turning the shoal into an artificial island or militarizing it. That is going to be very troubling,” Malaya said.

“The legal status of Scarborough Shoal as part of Philippine territory is clear. That is a red line," he added.

Further, Malaya expressed hope that China will continue to uphold the Declaration on the Conduct (DOC) of Parties in the South China Sea, the first political agreement jointly issued by the Association of Southeast Asian Nations (ASEAN) and China in 2002, aimed at maintaining stability in the region, pending the finalization of the Code of Conduct (COC).

Malaya cited a key provision of the 2002 DOC, which states that no party should occupy new maritime features or escalate tensions.

“In the Declaration of Conduct. No new occupation of occupied features. We expect China to adhere to that. They always mention the Declaration of Conduct in any statement by Beijing," he said.

"So, it is our hope that they will not go that far. That would be a red line for the Philippines,” he added.

On the other hand, Atty. Jay Batongbacal, Director of the University of the Philippines Institute for Maritime Affairs, emphasized that China’s repeated claims over Bajo de Masinloc lack any foundation in international law.

He pointed out that the 2016 Arbitral Award made it clear that the United Nations Convention on the Law of the Sea (UNCLOS) overrides any so-called “historic rights” asserted by China over the shoal.

The same ruling nullified China’s nine-dash line claim—now expanded to a ten-dash line—over nearly the entire South China Sea, affirming the Philippines’ sovereign rights in the West Philippine Sea.

Despite this, Beijing continues to disregard the decision.

“These are evidence that China is attempting to demonstrate that it is exercising control over the area. However, from a legal perspective, I would note that the area has been, admittedly, subject to dispute even by China, such control—legally—has no weight. Meaning, no matter how much control the exercise, as far as the legal situation is concerned, it has not changed," Batongbacal said.

He further explained that the status of Scarborough Shoal as Philippine territory is not defined by China’s current actions or attempts at control, but by the factual circumstances on the ground at the time the dispute significantly escalated in 2012.

“The earliest could be 1995, but whether it’s 1995 or 2012, what it means is nothing the parties do will affect the legal status of the shoal as of 1995 at the earliest or 2012 at the latest,” he added.

Scarborough Shoal, also referred to as Bajo de Masinloc or Panatag Shoal, is located 124 nautical miles off the northwestern Philippine province of Zambales.

In contrast, it lies 472 nautical miles from China’s nearest landmass, Hainan Province.

Batongbacal then pointed out that even in early maps, Bajo de Masinloc has consistently been shown as part of Philippine territory.

“The Philippines has been exercising jurisdiction and sovereignty over the shoal over a long period of time. I am confident about the legal status of the shoal being part of Philippine national territory,” he said.

“Our inability perhaps to immediately stop China and its activities to control the shoal is not a reason for us to stop because the law clearly is on our side. If we persist, we definitely hope that the law will eventually prevail,” he added.

Scarborough Shoal has been disputed for years.

Although it lies within the Philippines' exclusive economic zone, it has been under China’s control ever since a lengthy standoff between the two nations in 2012.

Chinese vessels have maintained a presence around the shoal's lagoon, blocking Filipino ships and fishing boats from entering the area.