HANGZHOU - A recent chemical spill on the Xin'an River, a major source of drinking water for East China's Zhejiang province, has led five water utility companies to stop drawing water from the river, a spokesman with local environmental protection bureau said Monday.

As of noon on Monday, water supplies for at least 552,200 people living in counties and cities near the provincial city of Hangzhou have been affected, said Lao Xinxiang, a deputy director and spokesman for the Hangzhou Environmental Protection Bureau.

Authorities have been closely monitoring the river since late Saturday night, when a tanker truck overturned on a highway near the river, resulting in the spillage of the truck's load of carbolic acid. The chemical was washed into the river by heavy rains.

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The Xin'an River, which feeds into the Fuchun and Qiantang rivers, is the main source of drinking water for several cities in Zhejiang, including Hangzhou.

The Xin'an River dam has been discharging water at an increased rate of 1,239 cubic meters per second to dilute the spill. The previous water discharge rate was 268 cubic meters per second.

The river's concentration of carbolic acid, an industrial chemical used to create plastic and other materials, has dropped because of discharges of water in the upper reaches of the river, which have diluted the chemical.

Although supplies of drinking water in downtown Hangzhou have not been contaminated, some citizens have rushed to purchase bottled water, causing some supermarkets in the city to run out of bottled water.

The Hangzhou city government has called on citizens to store some water for daily usage.