A water-buying panic triggered by a chemical spill into a river in east China's Zhejiang Province continued Tuesday despite assurances from local authorities that drinking water sources were safe.

A tanker truck overturned Saturday night on a highway near the Xin'an River, a major source of drinking water for the province, resulting in the spillage of the truck's load of carbolic acid, an industrial chemical used to create plastic and other materials.

About 20 tonnes of chemical was washed into the river by heavy rains. The accident led five water utility companies to stop drawing water from the river, affecting 552,200 residents in two county-level suburban cities in the provincial capital of Hangzhou.

A round of panicked water buying swept the affected regions and also downtown Hangzhou on Monday. Anxious people rushed to stores and stripped the shelves of bottled water after the local government issued several notices to ask residents to store some water for daily usage.

The provincial environmental protection bureau announced in a statement Monday afternoon that the water was safe and the five water utility companies would restart taking water from the river, yet the hoarding of bottled water remains prevalent.

People lined up at the Xicheng store of the Wumart supermarket in Hangzhou Tuesday morning, wanting to buy bottled water. Customer service manager Zhang Zhijun said the store sold out more than 500 boxes of bottled water by 3 p.m. -- that sale of that amount would normally take 12 days.

"We are making emergency orders to the producers. We will buy as much as possible because all the stores are vying to buy water," Zhang added.

The river's concentration of carbolic acid has been dropping continuously because of discharges of water in the upper reaches of the river, which have diluted the chemical, local authorities said.

However, the concentration of carbolic acid at the accident site was still over 50 times higher than the safe drinking level, a sample showed Tuesday afternoon.

Yang Jianhua, an expert with Zhejiang Academy of Social Sciences said, should the local government have educated local residents on necessary knowledge about the chemicals shortly after the accident, there might not be such a widespread panic purchases.

The notices issued by the government asking residents to store water were also misleading, which in part exacerbated the severity of the accident, Yang said.