Ice has formed in the Amur River at Khabarovsk

"I'm appealing for the panic to stop," Aleksandr Sokolov said on local TV, after residents emptied the shops of bottled water.

An 80km (50-mile) stretch of water contaminated with benzene is flowing towards Russia from China.

Russian officials say the pollution may reach Khabarovsk around 1 December.

The authorities there say they have 70 water tankers ready to supply the city's residents with water if the mains system has to be shut down.

"I urge people not to try and profit from the situation and not to whip up anxiety," the mayor said.

Benzene can be lethal to humans, even in small doses. The Russian emergencies ministry estimates that the maximum period of heightened toxicity in the Amur river will be two weeks.

The toxic water will arrive first in Leninskoye, in the Jewish Autonomous Region, on 27-28 November, the ministry predicts.

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Earlier, a senior Russian official told the BBC that the mains supply of drinking water in Khabarovsk - taken from the Amur - would be cut off for several days.

A communications hotline has been set up between Chinese and Russian experts to monitor the benzene spill.

Khabarovsk is home to about 650,000 people and the authorities fear 1.5 million people in and around the city will be affected by the pollution.

Oleg Mitvol, deputy head of the Russian environmental monitoring agency Rosprirodnadzor, told the BBC that in Khabarovsk "the water supply will be shut off, because the purifying equipment cannot deal with benzene".