The mayor of Changzhi, where a chemical leak contaminated a river in Shanxi Province and threatened drinking water supplies of a million people, has apologized for the authority's delay in dealing with the incident.

Mayor Zhang Bao made the apology at a press conference held on Monday. He said the city government had underestimated the severity of the chemical leak after receiving the polluter's report on the accident on December 31.

The provincial authority did not receive the pollution report from Changzhi until five days after 9 tons of aniline was leaked into the Zhuozhang River by a local chemical plant.

An initial investigation revealed that a loose drainage valve was to blame for the leak.

Such pollution incidents are required by regulations to be reported to provincial authorities within two hours. The spill only became public on Saturday.

The contamination has affected drinking water supplies in downstream Handan in neighboring Hebei Province, which has a population of more than 1 million people.

Zhang said the government expected the company to clean up the spill in a timely manner.

According to the local emergency response headquarters an additional 30 tons of aniline had been contained in a nearby disused reservoir.

By Sunday, the concentration of aniline in the river decreased to 2.15 milligram per liter from the previous level of 72 milligram per liter. But the river water still cannot be used for drinking, as the national standard only allows less than 0.1 milligram per liter of the substance in potable water.

The delayed response of the contamination caused panic in Handan, where residents ransacked stores for bottled water.

Wang Yiping, spokesperson of the government of Changzhi, Shanxi Province, said previously that the local government do not have to report it to the provincial government if the contamination is contained within the city's geographical jurisdiction.

Changzhi is now using ground water sources to meet needs.

Xinhua