BEIJING— Workers in northern China dug diversion channels and used floating dams and solidifying agents to try to stop a diesel fuel leak that has polluted a large stretch of one waterway from flowing into the Yellow River, the water source for millions of Chinese.

More than 700 workers worked overnight into Sunday morning to contain a spill that leaked from a pipeline into the Wei River in Shaanxi province following a construction accident Wednesday.

The Wei is a major tributary of the Yellow River, China's second-longest, whose water quality has deteriorated rapidly as discharge from factories has increased and water levels drop because of diversion for booming cities.

Vice Premier Li Keqiang ordered local officials to "strictly prevent leakage and pollution from flowing into the Yellow River and ensure the safety of drinking water for the masses," according to a Shaanxi provincial government news release issued Sunday.

It said the fuel slick had been contained in the Wei and no threats to sources of water for human or animal use in the Yellow River had been discovered. Earlier reports said that, at its greatest extent, the fuel slick had spread out along a 20-mile (33-kilometer) stretch of the river.

Workers laid a total of 17 floating dams across the Wei to contain the leakage, and specialized chemicals were being spread to solidify the fuel and speed cleanup, according to a news release from the environmental protection bureau in the city of Weihai where the leak occurred.

Workers also dug diversion trenches opposite the site of the leakage to prevent accumulated fuel flowing downstream, the bureau said.

The pipeline's owner, China National Petroleum Corp., said it had plugged the leak in the pipeline and had removed a "large amount" of contaminated water, mud and sand.

"The amount of oil on the surface has noticeably dropped and the spread of the leak has essentially been brought under control," the company, China's largest producer of oil and gas, said in a news release.

There was no immediate word on disruption of supplies from the pipeline, a key fuel conduit which links the capitals of northwest Gansu province and central Henan province. A report Saturday from the official Xinhua News Agency put the amount of oil leaked at about 40,000 gallons (150 cubic meters).

The diesel leak is just the latest disaster to strike China's waterways, considered the world's most heavily polluted. More than 20 percent of water tested in nearly 200 Chinese rivers was considered unsafe for use, according to a report by the Ministry of Environmental Protection on the state of the environment in 2007.

One third of the Yellow River is heavily polluted by industrial waste and unsafe for any use, according to criteria used by the U.N. Environmental Program.

The Environmental Ministry has tried to shut down polluting factories along China's main waterways, but its power is limited because local environmental protection bureaus are under the control of local governments. (AP)