Nearly 2.5 million residents of a major city in west China have been ordered not to drink its tap water after the supply was contaminated with dangerous levels of a carcinogenic substance.
Panic buying of bottled water broke out in Lanzhou, the capital of Gansu province, on Friday after state media announced authorities had "detected excessive levels of benzene in [its] tap water system".
Officials found 200 micrograms of benzene per litre - 20 times the acceptable "national limit" - in samples of the city's water supply, according to reports.
Benzene, a colorless additive found in plastics, lubricants, dyes, detergents and pesticides, is a known factor in melanoma, leukemia and other cancers.
In China's worst case of river pollution, potentially cancer-causing chemicals, including benzene, spilt into the Songhua River in November 2005. The northeastern city of Harbin was forced to sever water supplies to 3.8 million people for five days.
The American Cancer Society reports that "Consuming foods or fluids contaminated with high levels of benzene can cause vomiting, stomach irritation, dizziness, sleepiness, convulsions, and rapid heart rate. In extreme cases, inhaling or swallowing very high levels of benzene can be deadly."