Philippine troops forcibly towed Chinese vessels allegedly cyanide fishing at a disputed reef in the South China Sea.

Filipino soldiers spotted the three Chinese fishermen near the military outpost BRP Sierra Madre in the Ayungin Shoal on Friday evening.

Two rubber boats from the Western Naval Command were deployed to detain the fishermen over the alleged security breach.

An inspection of the Chinese boat found four gallons of suspected cyanide believed to have been used for fishing.

Rear Admiral Roy Vincent Trinidad, Philippine Navy spokesman for the West Philippine Sea, said: 'It is detrimental to the environment. Not only for the fish, but also for the environment — the corals get destroyed.

'Cyanide is used on marine species to make them drowsy and unconscious. They're then caught alive, brought home, and sold, especially rare and expensive species.'

The Chinese men were towed out of the area using ropes and were released.

Trinidad added: 'They could have been arrested on a normal day, but since it happened at the BRP Sierra Madre, bringing them aboard would mean feeding and housing them, and they would see the ship's interior. So instead, we documented everything and confiscated the illegal materials.'

The BRP Sierra Madre is a grounded Philippine Navy ship at the Ayungin Shoal, serving as a military outpost to assert the Philippines' territorial claim in the South China Sea.

Authorities said a China Coast Guard ship was nearby but did not interfere during the encounter.

Expansionist China currently lays claim over almost the entire region, which is one of the world's busiest sea lanes. But a United Nations-backed tribunal in 2016 deemed its claims groundless.

The Communist rogue state - accused of genocide for its crimes against the Uyghur population - has been steadily increasing its influence in recent years through investment in developing countries.