Harbin (AsiaNews/Agencies) – Water supplies in Harbin , home to more than 3 million people, were cut off last night and will not resume "until further notice". Schools have been closed whilst many residents are trying to leave the cities because city authorities have warned that pollution is threatening the water supply, which comes from the Songhua River.

An assessment by the Heilongjiang Provincial Environmental Protection Bureau found the river had been contaminated by chemicals released by a massive explosion at the Jilin Petroleum and Chemical Company plant in the city of Jilin on November 13.

However in the past two days, the city government released at least three different notices about water supplies suspension.

The first, issued on Monday night, said water supplies would be cut for four days due to maintenance work on the supply system.

In a second notice released yesterday morning, city authorities admitted that supplies would be cut for four days because of fears of chemical contamination from the Jilin explosion.

Last night's announcement did not give a time frame for the suspension, arousing speculation that it could last for more than four days.

The November 13 explosion in the Jilin chemical plant released highly toxic substances, killing at least five people and forcing the evacuation of more than 10,000 nearby residents. It also contaminated the partially frozen Songhua River with benzene and phenyl, which can lead to hepatitis, urinary tract diseases and possibly cancer.

Pollution is certain and will affect the whole Songhua River, said a local official who preferred to remain anonymous.

As of 11 pm local time, state-television in Harbin had not yet informed the public about the pollution, whilst the number of people affected by contaminated water had already filled up 15 hospitals.

The authorities had initially announced a four-day suspension, but now no one is sure how long it will last.

The city government remains confident though that there is enough water for the time being and that people have stocked up enough water to last them until after the emergency. It also announced that it was going to draw water supplies from other places and use underground water reserves.

Despite official reassurances, people are starting to panic buying up as much water and food as they can lay their hands on.

In Harbin sales of outbound rail and air tickets have risen by about 60 per cent. Everybody wants to leave and finding tickets is getting harder, according to one plant manager. Every possible container in the plant has been filled up with water.

A saleswoman from the city's biggest supermarket, Carrefour's Yongping branch, said it had sold out of bottled water by about 3 pm yesterday, just one day after fresh stocks arrived.

The authorities expect to have brought in 2,000 tonnes of water by Monday. The city of Shenyang, the capital of neighbouring province of Liaoning, is planning to ship another 600.

However, all this won't make up for the shortfall in a city that uses 18,600 tonnes of water daily.

What is more, school authorities have cancelled classes till next Wednesday, an indication that the crisis might last longer than expected and that damages might be greater than forecast.

The 1,927km-long Songhua River winds its way through more than 30 cities and towns in the China's north-east. None of them, except Harbin, has announced that water supplies would be cut off.

Industrial pollution and environmental disasters have become front-page news in China. The massive explosion at the petrochemical plant in Jilin was but one among many. On December 23, 2003, a gas leak in Kaixian County officially killed 234 people. At the time, poor maintenance was blamed for the accident.