The warning came as millions of residents in the northwestern city of Harbin endured their third full day without running water after supplies were cut following the accident.

 

The slick, thought to be about 80 km long, continued to flow through the city on Friday along the route of the Songhua river, which supplies most of Harbin's tap water.

 

In Beijing government officials tried to reassure Harbin's 3.8 million residents that water supplies will resume quickly and safely.

 

However, locals say many residents are evacuating the city while engineers are contining to sink dozens of wells.

 

In a sign of how the city's water crisis has jarred China's nerves about pollution, Premier Wen Jiabao ordered authorities to ensure everyone has access to safe drinking water.

 

However, trust in the government's effectiveness in dealing with the spill received a further knock on Friday with a newspaper report that environmental protection officials initially tried to cover-up the extent of the pollution.

 

According to the China Youth Daily officials discharged water from a reservoir into the Songhua river in an attempt to dilute the spill following the explosion at the chemical plant.

They then decided not to warn the public about it.

Health impact

 

The government has since admitted 100 tonnes of benzene and nitrobenzene, about 10 tanker-truck loads worth, spilled into the Songhua after the blast.

But while officials have tried to play down the effects of the spill, environmentalists are warning the environmental and social impact of the disaster could be severe and last for years.

 

Kenneth Leung, an eco-toxicologist from the University of Hong Kong, said benzene would settle in the river sediment and be taken into the food chain by tiny fish which scour the river bed for food.

 

"Those higher up in the food chain such as water birds and humans could suffer," Leung said, explaining that animals can easily accumulate benzene but are unable to metabolise, or dispose of, the chemical.

 

Long-term danger

 

Leung added: "Benzene can bond to DNA and cause mutation which can lead to cancer."

"Benzene can bond to DNA and cause mutation which can lead to cancer"

Kenneth Leung,
Eco-toxicologist from the University of Hong Kong

His colleague, Dr Gu Ji-dong, said the pollution could pose a danger for several years after the slick had passed.

"With these class of chemicals, some of the micro-organisms can be degraded but some cannot," Gu said.

In an accident bearing many similarities to the Jilin blast, state media reported on Friday another chemical plant had exploded, this time in the nation's southwest Chongqing municipality on Thursday.

 

One worker was killed and at least 10,000 evacuated amid another feared benzene leak, the China Business News said.

 

Government officials refused to comment.