Drinking water supplies for more than 2 million people were apparently affected by an oil leak in China.

The state news outlet reported crude oil leaked from a pipeline, contaminating the water source for a water plant supplying the city of Lanzhou in northwest China.

An environment official said on Saturday this left hazardous levels of benzene in the city’s tap water, reported Xinhua news agency.

Benzene comes from crude oil and is a colourless, flammable liquid which can increase the risk of cancer.

Shops ran out of bottled water and fire engines were said to have been drafted in on Friday to bring clean water to panicked residents. By Saturday the local government is said to have stopped the emergency supply of drinking water.

The city’s environmental protection chief Yan Zijiang pinned the blame on a leaky pipeline owned by a subsidiary of state-run oil firm China National Petroleum Corporation, reported state media.