Chinese officials have warned of a severe threat to wildlife from one of the country's worst reported oil spills as an army of volunteers was dispatched to beaches to try to head off the black tides.

At least one man has drowned in crude during the clean-up operation, which has expanded as the area of the slick has doubled in size despite earlier government assurances that it was being contained and posed no risk to ecologically sensitive areas.

Five days after a pipeline explosion at the north-east port of Dalian, oil had reportedly spread over an area of 430 square kilometres, prompting a dispersal mission along the coast.

Hundreds of local volunteers are spreading absorbent matting along the Yellow Sea shoreline in an attempt to stop the slick from damaging beaches.

Out at sea, authorities have started to use oil-consuming bacteria to try to disperse the slick, along with chemical agents and lengthy floating barrages.

Even though maritime officials have mobilised 800 fishing boats to assist the 40 specialist vessels in the operation, the winds and tides are spreading the slick wider and thinner.

The difficult conditions have proved fatal for at least one man. A 25-year-old firefighter, Zhang Liang, drowned on Tuesday when a wave threw him from a vessel, according to the state news agency Xinhua.