BEIJING has dismissed as "fabrication" allegations that Chinese fishermen were using cyanide to destroy the Filipinos' fishing grounds in the Bajo de Masinloc atoll in the South China Sea.

The Philippines and China both claim Bajo de Masinloc or Scarborough Shoal as part of their territory.

"This claim is sheer fabrication. China has indisputable sovereignty over Huangyan Dao (Scarborough Shoal) and its adjacent waters," said Mao Ning, China Ministry of Foreign Affairs spokesman.

This file photo shows Filipino fishermen were spotted over Bajo de Masinloc during the aerial surveillance of the Philippine Coast Guard (PCG). Photo from Philippine Coast Guard

The Bureau of Fisheries and Aquatic Resources (BFAR) on Friday said Chinese fishermen have been using cyanide to intentionally destroy the traditional fishing grounds of Filipino fishermen.

"The Chinese government attaches great importance to the protection of eco-environment and conservation of fishing resources and resolutely fights against fishing activities that violate laws and regulations," Mao said in a briefing on Monday.

The Chinese Embassy in Manila on Monday night released the transcript of Mao's briefing to local media.

"Such continuous disinformation has led up to nothing but exacerbation of the maritime tensions and destabilization of bilateral relations," the embassy said.

"The groundless speculations, slanders and inconsistent statements of spokespersons of relevant Philippine agencies can only place their professionalism and credibility in doubt," it said.

It urged the "relevant Philippine agencies to handle maritime issues with all seriousness and meet the Chinese side halfway in safeguarding bilateral relations as well as peace and stability in the South China Sea."

On Tuesday, President Ferdinand Marcos Jr. said the Philippines would file a case against China if there is enough evidence of cyanide fishing in the Bajo de Masinloc.

Speaking to reporters on the sidelines of the 16th Ani ng Dangal 2024 in Manila, Marcos said: "If we feel that there is enough ground to do so, we will [file charges]."

He said he tends to believe the allegation.

"The BFAR said cyanide was really used; others say cyanide fishing has been done for a long time already. And I do know that there are cases of cyanide fishing before, even here in the Philippines," Marcos said.

What is alarming is "it has become more prevalent," the President said.

BFAR has also reported that Vietnamese fishers also use cyanide in Bajo de Masinloc.

The damage to the atoll's coral reefs from cyanide use compromises the entire marine resources, including other countries' waters, it said

In October last year, Justice Secretary Jesus Crispin Remulla said an environmental case against China might be filed in early 2024.

"We have evidence. It's just a matter of organizing the evidence and showing it to the proper tribunal. That's the most important, that we file a case before an international tribunal about the environmental damage caused by China," Remulla had said.

He said the Philippines' position is backed by the 1982 United Nations Convention on the Law of the Sea (Unclos).

China has built artificial islands at Cuarteron Reef, Fiery Cross Reef, Subi Reef, Hughes Reef, Gaven Reef, Johnson Reef and Mischief Reef in the South China Sea to reinforce its claim.

Manila and Beijing are signatories to the Unclos, but a 2016 ruling of the Permanent Court of Arbitration rejected the latter's claims in the South China Sea.

China refuses to recognize the arbitral ruling.