A tributary of the Yanhe River in northwest China's Shaanxi Province was polluted by crude oil leaked out from a pipeline, according to local sources yesterday.

A pipeline belonging to the fourth oil extraction factory of the Changqing Oil Field was broken by landslide at 7:30am yesterday, from which leaked oil spread quickly to the lower reaches of the Xingzihe River.

In the Jingbian County of the Yulin City in northern Shaanxi, slick was found in eight kilometers of the river, said Cao Xizhong, vice head of the county. Clean-up crew has managed to plug up the cracks and people are building dams to contain the oil.

In the adjacent Zhidan County of Yan'an City, people have built 16 dams and took back about 20 tons of oil by 1pm, said a local official.

Heavy rains in Yan'an added difficulty to the work. Local environmental protection bureau urged the clean-up crew to ensure safety of water in the Wangyao reservoir, which provides drinking water for the city.

Yanhe River is a tributary of the Yellow River, the country's second longest.