China said the blast had caused "major pollution", spilling benzene compounds into the Songhua River from which Harbin, capital of Heilongjiang province and home to nine million people, draws its drinking water.

Russia's environmental protection agency said on Wednesday it feared that the pollution would affect drinking water supplies in its Khabarovsk region, which the Songhua enters several hundred kilometres (miles) downstream from Harbin.

"The Chinese side attaches great importance to the harm and impact this pollution may bring our neighbour Russia," Foreign Ministry spokesman Liu Jianchao told a news conference.

"The Chinese side is actively taking measures to strengthen monitoring, treatment and observe the quality of water so as to minimise the harm caused by pollution," Liu said.

China's official Xinhua news agency quoted vice environment minister Zhang Lijun as saying: "The two sides are making specific arrangements for opening a hotline for the matter."

Russia's ambassador to China, Sergei Razov, confirmed plans for a hotline but played down the threat to Russia posed by the chemical spill.

"The Chinese assume that the contaminated water will reach Russian territory by Dec. 8," Russia's First Channel showed him saying after a meeting with Chinese officials.

"But by then, for natural reasons, including the fact three major rivers flow into the Sungari (Songhua), the concentration of harmful substances should go down to normal."

Russia's Emergencies Ministry said tests showed that no dangerous substances had yet reached the Amur river in Russia but continual checks were being carried out.

Russia's environmental watchdog said officials would make sure there was enough to drink.