BEIJING - A nine-kilometre (5.6-mile) slick of crude oil that spilled from a storage tank into a river in northwest China has been controlled by a clean-up crew of about 600, the Xinhua News Agency reported.

An official with the Zhidan county government in Shaanxi province said about the crew has recovered about 90 percent of the four tonnes of crude oil that spilled into the Zhouhe River last Friday, the news agency said.

Workers at Yongning Drilling Co. in Zhidan county were cleaning a tank when another tank burst leaking 10 tonnes of crude oil, four tonnes of which spilled into the river, it said.

The clean-up crew built six makeshift mini-dams to prevent the slick from expanding, the agency said.

An investigation was under way, the Beijing News said.

Zhouhe is a tributary of the Luohe river which flows into the Yellow river, the country's second longest.

Last week, hundreds of villagers in the eastern coastal province of Shandong rushed to collect crude oil that spilled from a pipeline run by state oil firm Sinopec and sold it to small refineries for a profit, local media reported.