A Chinese city government has apologized for taking five days to report a chemical leak that has affected another city's drinking water supply.

Xinhua News Agency says the mayor of Changzhi in northern Shanxi province apologized at a news conference Monday. He said the polluter had informed the municipal government of the leak Dec. 31 but that they had underestimated its severity. Xinhua says the city was required to report the leak to the provincial environmental authority within two hours.

About 9 tons of aniline had leaked into a river and contaminated the water supply in Handan city in neighboring Hebei province by the time the incident became public Saturday. Xinhua says the water still couldn't be used Monday.

Aniline, used in manufacturing polyurethane, can be toxic to humans.