China said on Wednesday a chemical-plant explosion 10 days ago severely polluted a river that provides drinking water to Harbin, one of the country's largest cities.
Water service in Harbin where a city of nearly four million people, has been turned off and will remain off for at least four days.
Authorities say they hope to protect municipal pipelines from dangerous contamination by benzene.
Bottled water is being trucked into the city. The State Environmental Protection Administration in Beijing says the explosion 10 days ago in Jilin city, 380 kilometers from Harbin, sent an unknown quantity of benzene into the Songha River.
Five people died in the blast, but until now authorities had denied any pollutants were released.
Benzene, a highly toxic and flammable industrial solvent, is known to be a carcinogen, cancer-causing substance.
Scientists said they have measured benzene levels in the river at Jilin more than 100 times the safe level.
Information for this report is provided by AP, AFP and Reuters.