Hundreds of emergency workers are trying to contain the leak
Pollution from a broken oil pipeline in northern China has now reached one of the country's major water sources - the Yellow River, state media say.
Hundreds of workers had battled to contain the oil upstream, but officials discovered traces in the river itself.
The traces were found about 200km (124 miles) upstream from Zhengzhou.
Three counties in neighbouring Shaanxi province have warned people not to take supplies from the river or drink river water.
Correspondents say local towns and cities get some of their water from the river, the rest from underground water sources.
The official Xinhua news agency said: "At present, cities along the river in Henan province have sufficient water resources."
About 150,000 litres of diesel poured into the Wei river in Shaanxi province after a construction accident on Wednesday, state media reported.
The leak occurred on the fuel pipeline operated by the state-run China National Petroleum Corporation (CNPC) that connects Lanzhou in the north-west province of Gansu with Zhengzhou in central Henan province, according to the China Daily newspaper.
The diesel first went into the Chishui river, a tributary of the Wei.
Around 700 emergency workers are said to be labouring round the clock, using floating dams and solidifying agents to contain the spill.
Their task has been helped by the current cold weather in the region.