"Mass incidents" -- protests and riots in the ruling Communist Party's jargon -- over environmental woes have grown at an annual rate of 29 percent in recent years, he said.

After two decades of breakneck economic growth, China has 20 of the world's 30 most polluted cities, the World Bank says. An estimated 300 million nationwide have no access to clean water.

Zhou was appointed in December after his predecessor was forced to resign over his handling of a toxic spill that poisoned the Songhua River, a source of drinking water for millions.

The degradation of the environment has increasingly galvanised citizens across the country into violent actions because of the slim chance of redress through legal channels.

Zhou did not give an exact number for the protests, but said there were 51,000 pollution "disputes" last year alone.

Thousand of villagers rioted in Zhejiang province last April, forcing the closure of 13 polluting chemical plants. About 50 policemen were injured and four protesters were later jailed.

An eastern industrial stronghold, Zhejiang was hit by at least two other mass protests in 2005, one of which also ended with the shut-down of a battery factory.

A Hong Kong newspaper reported that about 200 villagers in the southeastern province of Fujian, angered by pollution of their water supply, attacked three factories and a sewage treatment plant earlier this month.

At pains to avoid social unrest, the government has made balanced growth and greater respect for the environment a key element of a development plan for the next five years.