ASEAN Beat | Security | Southeast Asia

Philippines Accuses China of Cyanide ‘Sabotage’ at South China Sea Shoal

Philippine security officials claim to have discovered plastic bottles of cyanide on Chinese boats close to Second Thomas Shoal in the Spratly Islands.

A photo released by the Armed Forces of the Philippines that claims to show a China Coast Guard vessel firing a water cannon in the vicinity of Second Thomas Shoal in the South China Sea, Aug. 20, 2025.

The Philippines yesterday accused Chinese fishermen of dumping cyanide in waters around a contested atoll in the South China Sea in a bid to loosen Manila’s hold over the feature, drawing a fierce denial from Beijing.

In an interagency press briefing in Manila, Philippine security officials said that they had discovered cyanide on Chinese boats close to Second Thomas Shoal, a submerged reef in the Spratly Islands that was the focus of tense stand-offs between the two nations’ coast guards in 2024 and 2025.

Laboratory tests confirmed the presence of the toxic substance in bottles seized by the Philippine Navy last year at the atoll, which Manila refers to as Ayungin Shoal, the officials said.

“The yellow bottles seized from the sampans contain cyanide, a highly toxic chemical known to cause severe damage to human and maritime systems,” Gen. Cornelio Valencia Jr., the assistant director of the National Security Council, said during the briefing, as per Rappler.

Valencia said that the cyanide could have had serious consequences for marine life in the area and threatened to weaken the integrity of the reef supporting the BRP Sierra Madre, a grounded Philippine Navy warship that serves as Manila’s outpost at the atoll.

Sodium cyanide is sometimes used in fishing, since the chemical stuns the fish without killing it, making it easy to catch in a net, or even by hand. The Philippine authorities have previously accused Chinese fishermen of using cyanide to catch fish at Scarborough Shoal, another disputed shoal in the South China Sea.

In this case, however, Valencia alleged that the use of cyanide had a more nefarious goal. “We wish ⁠to underscore that the use of cyanide in Ayungin Shoal is a form of sabotage that seeks to ​kill local fish populations, depriving Navy personnel of a vital food source,” Valencia added.

The officials said that there are at least four documented instances from February 2025 to March 2026 in which Filipino soldiers who were deployed to the BRP Sierra Madre........

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