China's environmental woes are so large they've begun to generate social instability.

Choking on vile air, sickened by toxic water, citizens in some corners of this vast nation are rising up to protest the high environmental cost of China's economic boom.

In one recent incident, villagers in this hilly coastal region grew so exasperated by contamination from nearby chemical plants that they overturned and smashed dozens of vehicles and beat up police officers who arrived to quell what essentially was an environmental riot.

"We had to do it. We can't grow our vegetables here anymore," said Li Sanye, a 60-year-old farmer. "Young women are giving birth to stillborn babies."

Across China, entire rivers run foul or have dried up altogether. Nearly a third of cities don't treat their sewage, flushing it into waterways. Some 300 million of China's 1.3 billion people drink water that is too contaminated to be consumed safely. In rural China, sooty air depresses crop yields, and desert quickly encroaches on grassland to the west. Filth and grime cover all but a few corners of the country.

China's central government isn't sitting still. It's enacting fuel-efficiency requirements for vehicles and shutting down mammoth dam-building and other projects. By some accounts, it now has world-class laws on environmental protection.

Yet provincial and local officials, who feel pressure for economic growth, often shield polluters and ignore environmental laws.

"The policies from the top are not carried out at the bottom," said Niu Yuchang, a peasant organizer in Beijing who hears many environmental complaints. "The [local] officials care only about development. They don't care about water or air pollution."

Most of China's cities have a local environmental-protection bureau, but powerful city officials sometimes bully the civil servants who run them.

"It is so embarrassing that some of them even have to write anonymous letters to us to denounce local environmental problems," said Wang Jirong, the vice minister of the State Environmental Protection Administration, a national watchdog.

China's leaders have known for years that pollution is taking a toll on public health and crimping economic development, but the notion that dirty air and water might spawn social unrest is relatively new.

Environmental riots, such as the one that erupted in this village two hours' drive south of Hangzhou, underscore the severity of the pollution and that local officials can let economic goals trump concern about pollution. Some citizens felt as though they had their backs to the wall.

"These people spent over a year trying to tap legal channels before [they acted], and that's the story repeatedly," said Elizabeth Economy of the Council on Foreign Relations in New York and author of "The River Runs Black," a book on China's environmental crisis.

"They try through various means to get a response or to get the factory shut down. And the local officials just close their ears," Economy said.

Farmers riot

Huaxi (pronounced wha-she) is tucked amid rolling hills in coastal Zhejiang province, where industrial parks have sprung up amid rice paddies and corn, turnip and celery fields.

A few years ago, officials in the surrounding Dongyang township took 85 acres from Huaxi farmers to build chemical and pesticide plants, an industrial grease factory and a paper mill.

The state-owned plants produce weed killers and fluorene, a toxic chemical.

By early last year, farmers complained of burning eyes and withered crops. By this spring, stunted cabbage in the fields had turned yellow.

"It's rotten from the inside. It doesn't grow," said Li Xian, a 39-year-old farmer.

A putrid, irritating chemical smell wafts in the air.

"The smell is extremely bad. It's just awful. I can't describe it. Everybody complains about it," said another farmer, Wang Huida.

Villagers, many of whom lost land when the industrial park was built, grew angry enough that they built a tent camp near the park in early April and threw up obstacles on a road.

"We tried to block the chemical factories from normal production," Li Sanye said.

Organizers rallied elderly protesters, calculating that police wouldn't move against them under a "put people first" policy put forth by Premier Wen Jiabao, who took office in 2003. It was a mistake. Before dawn April 10, buses and vans with hundreds of police aboard rumbled into the village. Police pulled down the tent camp.

Irate elderly peasants, all women, lay in the road in protest.

Rumor spread that a police vehicle ran over two elderly women. Protesters shot fireworks into the air, drawing surrounding villagers, and mayhem erupted.

"The local people beat anyone they could catch wearing a uniform," Wang said. "Some 50 or 60 vehicles were overturned."

Police retreated, and for days after the riot, the village was littered with the hulks of overturned cars, some draped with police uniforms that had been stripped from those who fled.

Alarmed by the uprising, authorities imposed a news blackout, and only a few Internet postings survived.

Regional officials have sacked a township deputy mayor and promised to move the most noxious polluting factories to another area, according to subsequent news reports that didn't mention the rioting.

Urban population rises

Even amid signs that the deterioration of air and water quality might have slowed, new pressures are coming to bear, primarily from massive migration to cities.

China's urban population is expected to grow from around 520 million people now to 850 million by 2015, according to the World Bank, putting huge new pressures on water supplies, urban waste treatment and air quality.

President Hu Jintao has abandoned a decades-old approach of developing the economy first and worrying about the environment later. He's urged local officials to seek sustainable "green" development.

But he's offered no acknowledgment that environmental constraints might hinder his goal of expanding the economy fourfold by 2020.