LUCHENG - Nearly 9 tonnes of aniline leaked by a chemical plant in North China's Shanxi province have ended up in the Zhuozhang River, local authorities said Sunday.

An initial investigation revealed that a loose drainage valve in the plant, which is owned by the Tianji Coal Chemical Industry Group, was to blame for the leak.

The leak was discovered on Dec 31, 2012, when plant employees spotted aniline leaking from a broken pipe while conducting a routine check, a company spokesman said.

Another 30 tonnes of spilled aniline have been contained in a nearby disused reservoir, the local emergency response headquarters said.

A statement from the municipal government of Changzhi said the leak has not resulted in any deaths, adding that the river's water quality has been improving.

A further investigation into the accident is under way.

The contamination has cut off water supplies for Handan, a city located on the river's lower reaches, since Saturday afternoon. The city government said water supplies will not be immediately resumed.

Aniline is a toxic chemical widely used to manufacture pigments, herbicides and other chemicals.

Other rivers have experienced similar contamination in recent years. The Longjiang River in South China's Guangxi Zhuang autonomous region was polluted with industrial waste in January 2011, killing a lot of fish and cutting off water supplies in the city of Liuzhou.

In 2010, the Songhua River in Northeast China's Jilin province was polluted by chemicals that were swept into the river after floods hit warehouses owned by two chemical companies.