As many as two dozen people became ill after a tanker carrying toxic chemicals overturned and went into a river in Qingwan, a town in south China's Guangxi Zhuang Autonomous Region, on Wednesday. 

Some of the victims apparently breathed poisonous gases in the wake of the accident, and were taken to a hospital for treatment.

No deaths were reported.

Nearly 1,000 villagers in the town, which lies in the Guangdong-Guangxi border area, were immediately evacuated to safety.

Qingwan, in Guangxi's Yulin Prefecture, is located in less than a kilometre from Huazhou, a city in western Guangdong Province.

The truck carried more than 40 tons of benzene before it overturned on a highway at a turn and plunged into the meandering Lingjiang River.

More than 10 tons of the toxin were believed to have escaped into the Lingjiang, a major source of drinking water for area residents.

Water supplies in major towns and villages for 20,000 people in the Guangdong and Guangxi areas have been suspended for about two days due to the serious contamination, a Maoming Municipal Bureau of Environmental Protection official told China Daily yesterday.

"No one can tell when the water supplies will be resumed," the official who asked not to be named said.

"We need to conduct more tests to ensure the water quality meets the State's drinking standard," the spokesman said.

While waiting for reports from further tests of sample of the contaminated water in the river, environmental protection departments are now paying close attention to any further findings of the water quality of river, the official said.

Authorities are urging residents not to drink the water nor eat its aquatic life in the immediate future.

The tank and truck engine were seriously damaged in the wake of the accident, causing a heavy traffic jam in Guangdong-Guangxi border area in south China.

The truck and the oil tanker were separated after the accident, with a major traffic tie-up ensuing. The driver of the truck survived.

Local investigators immediately arrived in the site for the recovery work.

Police blockaded the site for further investigation and prevented local people from getting near the toxic chemicals.

All site personnel wore specialized gear to protect them from the chemical products, which were estimated to have covered an area of more than five square kilometers.

The cause of the accident was likely excessive driving speed and a slippery road surface after successive days of rainfall.