The Nairobi-based UN Environment Programme (UNEP), which sent a team to China's northeast to investigate damage to the Songhua River and surrounding areas caused by the November spill, said Chinese authorities had reacted too slowly to inform the public of the dangers.

"It is clear that, during the initial response phase, government communication and information sharing with the general public was not adequate enough to ensure appropriate responses of the affected population," UNEP said in its report on the incident.

UNEP suggested that China work with it to implement an emergency response plan for local authorities who did not disclose that the river had been contaminated until 10 days after the spill, which was caused by a massive explosion at a benzene factory on November 13.

"Further investigations are needed to clarify whether existing early warning systems and contingency plans were sufficient," the report said. "Furthermore, an analysis of the internal risk management practices of industry should be undertaken... to assess the state of preparedness and identify capacities and legislation or regulations required to minimize the risks."

UNEP said it was ready to assist the government in Beijing, adding that China and Russia should cooperate on emergency response and disaster contingency plans as well as share chemical analyses, including air quality samples, from areas affected by the spill.

Senior Chinese officials and the parent company of PetroChina, whose benzene plant exploded, have apologized for the environmental crisis which shut down water supplies for up to four million people in Harbin, one of China's largest cities, for five days.

The 80-kilometer-long (48-mile) slick of highly toxic and carcinogenic benzene flowed through Harbin along the icy, 1,897-kilometer (1,178-mile) Songhua which provides the city and surrounding population of nine million with much of its water as well as more than a million people across the border in Russia.

Fifty tonnes of chemicals, mostly benzene and nitrobenzene, are believed to have been absorbed in the river bed and deposited along the banks above Harbin while the other 50 tonnes from the explosion were thought to have passed through the city, posing risks for Chinese further downstream and people in Russia.

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