LANZHOU, April 10 (Xinhua) -- Oil from an unidentified source leaked into a water channel linking to the Yellow River in northwest China's Gansu Province, authorities said Friday.

The environmental protection bureau of Lanzhou City has been cleaning the oil from the water channel, which was previously used to discharge floods from the Yellow River.

A spokesperson with the bureau said pollutants in the nearby Yellow River have not been detected and authorities have cut off water supply from the river.

On Friday morning, Xinhua reporters at the site saw two workers collecting the oil, which was leaked from the crevice of the levee.

A gas station near the water channel was closed Thursday, but it is unsure if the oil leakage was related to the station, the spokesperson said.

The bureau plans to dig out the levee to further investigate where the oil came from, he said, adding that the unidentified oil was found on Thursday morning.

However, according to a domestic media report, residents in Lanzhou had claimed that oil was found on the water of the channel and spread pungent smells in early March.