Two oil tankers have collided in waters off Guangdong province, causing a major oil slick.

There are fears the spillage will pose a serious threat to marine life in the area, including the endangered white dolphin.

The white dolphin is actually pink

China's state media said diesel-oil poured into an area near the mouth of the Pearl River on Friday.

Both tankers were carrying thousands of tonnes of oil. Two tanks on one vessel were badly damaged, each with a capacity of 1,000 tonnes of oil.

The oil formed a slick reported to be about 10km long and five metres to 50 metres wide.

A spokesman for the World Wide Fund for Nature in Hong Kong told the BBC that the environmental damage caused by the spill would depend on the exact amount of oil leaked and what action the authorities had taken to contain it.

But she warned it could have a major impact on the ecology of the whole estuary, which is a rich fishing ground as well as one of the last strongholds of the Chinese white dolphin, which is listed as an endangered species.

There are also fears of a possible threat to Hong Kong's Mai Po marshes, a protected breeding-ground for sea birds.

Chinese officials said the spill would take weeks to clear. The white dolphin has been declining in recent years because of the increase of pollution in southern Chinese and Hong Kong waters and the construction of the new Hong Kong airport, which disrupted a dolphin habitat.