The explosion happened 10 days ago at a chemical plant, causing pollutants to leak into the Songhua River, which runs through Harbin -- a city of several million people.
China's Environmental Protection Administration says that benzene levels in the river are now 108 times the national safety levels. Benzene is a toxic industrial solvent.
Heilongjiang Province Governor Zhang Youyi, speaking in Harbin, said the authorities are dealing with the crisis as a priority.
"The contamination of the waters of the Songhua River has led to the shutdown of water supply to a city of a few million people," Zhang said. "This is a matter we must not take lightly. Officials from the various authorities must treat this matter with utmost importance and see to it that we can resume our water supply to the city."
Russian officials today expressed concerns over a possible pollution threat to the city of Khabarovsk, which has a population of some 700,000 and is located about 700 kilometers downriver from Harbin.
The Songhua River runs into the Amur River, which forms a long section of the Chinese-Russian border.
(Reuters/AFP/Chinese state media)