Thousands of angry Chinese protesters took to the streets of Weiyuan in the southwestern Chinese province of Sichuan on Tuesday amid growing popular anger over the leakage of toxic gas from a nearby chemical plant, local residents said.

"[There are] several thousand people [here]," a protester surnamed Hu from Weiyuan county told RFA, adding that the protests were linked to a gas leak at the coking plant, just 800 meters from people's homes.

"After the leak, the authorities just did nothing even though the factory is just 800 meters away, and some kids had shown adverse reactions," Hu said.

"The parents want an explanation of what happened from the government, which initially said a coagulation agent had leaked, and then said it hadn't," she said.

"People were very unhappy with the government's response, so they started demonstrating," Hu said. "The high-schoolers came along as well today."

"They pushed down the gates [of their school] and some kids were hurt," she said. "They also overturned a police vehicle."

Security forces had begun sealing off nearby roads, but officials had still done little to ease the standoff, Hu said.

"Some county government officials came out and said a few words and went away again," she said.

'Leave soon'

An official who answered the phone at the county environmental protection department declined to comment on the air quality in Weiyuan.

But the official added: "We are advising residents of Chengnan district [of the Weiyuan county town] to leave the area as soon as they can."

However, a duty officer who answered the phone at the Weiyuan county government offices on Tuesday said emissions from the plant had returned to safe levels.

"The air quality here is fine now; there is no danger to human health," the official said.

"We have set up a special task force [to deal with this]."

Scenes of chaos

Fellow protester Luo Yong described scenes of "chaos" outside the county government buildings in Weiyuan on Tuesday.

"They are sending a task force down from the provincial government and the Chengdu municipal government," Luo said.

"People have already started rioting here, and the city and county authorities have sent more than 1,000 police to suppress it," he said.

"They beat the kids back into the high school campus earlier this morning, and some of the students were injured," Luo said.

He said the protests had begun peacefully on Friday, but had turned violent late on Monday.

He said foul-smelling gases have continued to waft over from the chemical plant.

"The government is trying to cover it up, and to lie to us," Luo said. "Some people are in the hospital, while others have come out in a red rash all over their bodies."

"The entire county town stinks of this gas after nightfall, and there are some plainclothes people going around getting people out of their homes and beating them up," he said. "I think they're hired by the factory."

He said "more than a dozen" people had been detained by police from Neijiang city on suspicion of "incitement."

"I have also been designated a suspect, and they have threatened me," Luo said. "I'm keeping a low profile ... [but] I can't tell you about it over the phone, because it's being monitored."

Reporting blocked

According to Hu, China's tightly controlled media has been prevented from covering the protest.

"The government has instituted a news blackout, and they're not reporting it," she said.

"Some of the students are in hospital with allergic reactions, red lesions, but the school has told them they mustn't go telling people that it's to do with the gas leaks."

"They have to say it's a medical problem of theirs."

Hu said the government has been broadcasting SMS messages to the local population calling on people to "behave rationally" and stop demonstrating, and promising to deal with the problem.

"But that process is too long and it's not very effective," Hu said.

Another demonstrator surnamed Xiao said the high-school students were largely behind the overturning of police vehicles and the storming of their school gates.

"They were pretty energetic, because their school is pretty close to the coking plant," Xiao said.

"This factory has always released foul-smelling gases, but in the past few days the stench has been particularly bad, and it's still there today," he said.

Asked what protesters want from the government, Xiao replied: "We want the coking plant shut down."

Growing wave of protests

Worsening levels of air and water pollution, as well as disputes over the effects of heavy metals from mining and industry, have sparked a growing wave of mass public protests linked to environmental protection in recent years.

Last week, primary school children boycotted class to take part in mass protests in Langtang township in the southern province of Guangdong over plans to build a waste incinerator plant near their homes.

Campaigners across China have also raised growing concerns over the falsification of pollution testing and environmental impact assessments.

Activists say China has a comprehensive body of environmental protection laws, but that vested interests and collusion between local governments and business mean they are rarely properly enforced.