The Philippines detained 12 Vietnamese fishermen and their Malaysian-flagged boat for collecting endangered fish and sea turtles and poaching, an official said Wednesday.

The Filipino coast guard intercepted four fishing vessels in the Sulu Sea off the Malaysian state of Borneo late Sunday, but three escaped as the fourth was being boarded, fisheries bureau director James Perez said.

"Unfortunately we apprehended only one because the three other vessels resisted," he told AFP.

Officials found humphead wrasse, an endangered species of fish, on board the detained boat and about 50 sea turtles, including critically endangered hawksbill turtles, already dead and smothered in ice in its hold, he added.

"This is a Malaysian-flagged vessel, but the crew are Vietnamese," he said. "We have filed a criminal complaint against them."

The hawksbill turtle, Eretmochelys imbricata, grows up to 85 centimetres (33 inches) and can weigh up to 75 kilograms (165 pounds).

The International Union for the Conservation of Nature (IUCN) says it is "critically endangered" because it has been exploited for years as the sole source of commercial tortoise shell.

The humphead or Napoleon wrasse, Cheilinus undulatus, which grows up to 2.3 metres and weighs up to 191 kilogrammes, is one of the world's largest reef fish.

Swiss-based IUCN classes it as "endangered" and says its numbers have fallen hugely over the past 30 years, a situation that it predicts will accelerate further due to rising live fish demand.

Catching or trafficking in critically endangered Philippine species is punishable by a six-year prison term and a million-peso ($23,000) fine, the environment department said.