Water supplies to 28,000 people in northern China have been cut after an overturned truck spilled 33 tons of toxic oil into a river, state media said Wednesday, the latest mishap to degrade the country's already polluted waterways.

The overloaded truck was carrying wash oil, also known as creosote, when it overturned and dumped its contents into a river in Shanxi province, Xinhua News Agency reported.

The spill flowed into the Yangjiapo reservoir, contaminating 70 million cubic feet of water, the agency said, citing the provincial environmental bureau.

Supplies to the towns of Dazhai and Sandu in Xiyang county, which the reservoir serves, have been cut, Xinhua said.

Creosote is commonly used to treat wood products and probably causes cancer in humans, according to the U.S. Agency for Toxic Substances and Disease Registry.

The spill occurred last Thursday, Xinhua said, but did not say why it was reported a week later.

Cleanup crews were using pumps, tons of activated carbon and other materials to absorb the spill of brown oil, the agency reported.

To provide a temporary supply, local authorities were trucking in drinking water to affected residents, and were attempting to connect water pipes to a large well in the nearby village of Mahui, Xinhua said.

Investigations showed the truck overturned due to brake failure, the report said.

Most of China's canals, rivers and lakes are severely tainted by agricultural and household pollution. Chinese leaders say the country faces a critical water shortage, in part because of chronic pollution and chemical accidents.

In August, China said it would spend 125 billion to improve water treatment and recycling by 2010 to fight the mounting threat of urban water pollution.

Last November, a chemical plant blast spilled tons of benzene and other toxic material into the Songhua river, halting water supplies to millions in China and Russia. Local authorities were accused of reacting too slowly and delaying public disclosure of the spill.