Chinese environment officials are rushing to build three temporary barriers on the Yellow river after failing to contain an oil slick in a tributary of the country's second largest waterway.

Despite overnight efforts by 700 workers to dig diversion channels, the contamination belt — which was 13 miles long at its peak — has tainted the giant Sanmenxia reservoir, the state media reported today . Some areas have been forced to suspend water supplies according to the Xinhua news agency, as the spill spread from the Wei tributary in Shaanxi province to the Yellow river in Henan province.

Separate reports said the major downstream cities of Zhangzhou and Kaifeng would not be affected as they have alternative water supplies.

The oil spill occurred last Wednesday when 150 tonnes of diesel leaked from the Lanzhou-to-Chengsha pipeline owned by the China National Petroleum Corporation, but it did not become known publicly until Sunday.

After the leak, the state-owned firm and environment ministry dispatched teams to the area to try to control the leak before it entered the Yellow river, which sustains 140 million people with water supplies for drinking, irrigation and industry.

As well as diversion ditches, they used 27 floating barriers to try to isolate the diesel so that it could be removed or soaked up with absorbent materials.

China's vice premier Li Keqiang said the operation should "strictly prevent leakage and pollution from flowing into the Yellow river and ensure the safety of drinking water for the masses," according to a news release at the weekend.

But today's monitoring data along the Yellow river indicate the efforts were only partially successful, with the already poor water quality deteriorating further.

The Sanmenxia dam has been closed to prevent the contamination from passing further downstream. Emergency teams are using the floating barriers to divert the spill to an area of the reservoir where it can be dealt with.

The environment department of Henan province said its senior officials has been dispatched to join the containment effort. "We don't have anyone here who can comment as they all at the site," said an operator at the head office.

The Yellow, often described as the Cradle of Chinese civilisation, is one of the country's most heavily exploited and polluted rivers. According to the United Nations, water is unfit for any use along one third of the river.