China on Monday asked the Philippines to ensure swift and fair treatment for six Chinese fishermen detained and facing up to 24 years in jail for allegedly poaching sea turtles in disputed waters.

China's foreign ministry spokesman said Beijing was "paying attention to the incident", had spoken to the Philippine side and had sent staff from the Chinese embassy in Manila to visit the detainees.

"We have asked the Philippine side to ensure the safety and legal rights and interests of the Chinese fishermen and handle the issue in an early and fair manner," spokesman Hong Lei told a regular press briefing.

The Chinese fishing boat was intercepted by the Philippine navy on December 1 off the coastal town of Balabac in Palawan, a western island facing a section of the South China Sea that both countries claim.

Police confiscated the boat and recovered 11 sea turtles, fishing nets and other paraphernalia from the six fishermen.

Philippine environmental authorities and police have filed charges against the six for illegally poaching an endangered species. They face over two decades in jail if convicted.

Hundreds of Chinese fishermen have been caught allegedly poaching in waters off Palawan over the past decade, but all have eventually been freed and deported to China, often under pressure from Chinese diplomats.

China claims ownership over all of the South China Sea on historical grounds, and its fishermen often stray close to Philippine shores.

In October, the Philippine navy seized 25 small Chinese fishing boats being towed by a larger vessel, also off Palawan.

The bigger vessel escaped after the navy confronted it near Reed Bank, just 150 kilometres (90 miles) from Palawan.

Taiwan, Vietnam, Brunei and Malaysia also have competing claims to parts of the South China Sea.

Vietnam and the Philippines have complained of increasing Chinese aggression in the area, but a proposal by Manila at a recently concluded East Asian summit seeking a stronger regional front against Beijing failed to gain traction.