The medical service provider International SOS has issued a health alert to people travelling in northwestern China, where a ruptured diesel pipeline is threatening drinking water in the country's second-longest river. The commercial medical agency warned travellers yesterday to stay alert when drinking water in areas affected by the oil spill. Last Wednesday, an estimated 100 tonnes of diesel fuel spilled into the Wei River, a major tributary of the Yellow River that runs through Shaanxi province. The broken pipelines, owned by state oil giant PetroChina, contaminated the Wei, posing a threat to the water supply of hundreds of thousa+nds of people. The huge leak was discovered in Chishui township, Hua county, which houses a big tourist attraction, Hua Mountain. Xinhua reported that China National Petroleum Corp, PetroChina's parent company, had shut off the pipeline, part of a 1,188-kilometre network carrying oil from Lanzhou in the northwestern province of Gansu to Zhengzhou in the energy-hungry central province of Henan . A channel was dug at the site to divert unaffected water, and barriers were set up to try to control the spill, but contamination reached the Sanmenxia Reservoir and hydropower station, located on the upper reaches of the Yellow River. A week after the leakage, Xinhua said the spill had been 'basically contained' in Sanmenxia Reservoir and caused no further contamination of the water in Xiaolangdi Reservoir and the downstream supply of drinking water. It also said part of the diesel fuel that leaked at a site close to the Chishui River had entered the Wei River and that experts were calculating the volume of the spill that had reached the Yellow River from the two tributaries. International SOS warned against drinking tap water in affected areas but said it would generally consider drinking tap water on the mainland to be unsafe even without the contamination alerts. Dr Chris Wong Kong-chu, an associate professor of biology at Baptist University, said drinking water containing a high concentration of diesel fuel could affect the oesophagus and other digestive organs, as it was a corrosive organic compound. However, Wong said human exposure was not common, as water contaminated with diesel usually had a sharp, foul odour that could be easily detected.