SHIFANG: A Chinese city has released 21 people who were detained after a clash between police and residents protesting against a metals plant they feared would poison them, city officials said on Wednesday, the second unusual official concession in two days.

Thousands of people in the southwestern city of Shifang took to the streets over the past three days against the government's plans to allow the building of a copper alloy plant, the latest unrest spurred by environmental concerns in the world's second-largest economy.

The Shifang government said police had "forcibly taken away 27 suspected criminals" on Monday and Tuesday for tearing down the door of the municipal government building, smashing windows, and throwing bricks and stones at police and government workers.

That prompted a massive sit-in on Tuesday night outside a government office by locals demanding their release.

Six are still in police custody, the city government said in a statement on its official Sina Weibo microblogging site.

"The remaining 21 people, after receiving criticism and education and repenting for their mistakes, were released at 11 p.m. on July 3," the government said on Wednesday.

The government took the uncommon step on Tuesday night of halting the metals project planned by Shanghai-listed Sichuan Hongda. The city initially had said it would only suspend the project.

The latest protest underscores how environmental worries have stoked calls for expanded rights for citizens and greater consultation in the tightly controlled one-party state. They follow similar demonstrations against projects in the cities of Dalian in the northeast and Haimen in southern Guangdong province in the past year.

PUNISHMENT DEMANDED

Despite the dual concessions, some Chinese called for the punishment of officials responsible for the violent crackdown. An 18-year-old resident told Reuters by telephone on Tuesday the police had beaten protesters the previous night.

"What are we going to do about the bastards who used violence on innocent people?" said microblog comment.

Said another: "You have beaten up a bunch of innocent people. Don't these leaders need to be criminally detained too? Release them!"

Photos of Tuesday night's sit-in protest published on microblogs showed a large crowd sitting down under street lamps, in what one microblogger described as "a sea of people" demanding the release of those detained.

The protests turned violent on Monday when tens of thousands of residents stormed the city government headquarters, smashed police cars and clashed with thousands of anti-riot police, which fired tear gas on protestors.

The outpouring of public anger is emblematic of the rising discontent facing Chinese leaders, who are obsessed with maintaining stability and struggling to balance growth with rising public anger over environmental threats.

The leadership has vowed to clean up China's skies and waterways, and increasingly tried to appear responsive to complaints about pollution. But environmental disputes pit citizens against local officials whose aim is to lure fresh investment and revenue into their areas.

"The best of you emigrate, the worst of you are shot," China's most famous blogger, Han Han, wrote on his blog, addressing Shifang officials. "But none of you actually live in the pollution. Only ordinary people live there."

"Shifang" remained the most searched term on China's Twitter-like microblogs on Wednesday. Chinese authorities, who are usually quick to suppress dissent from spreading, did not block searches related to the protests.

"It is the 4th of July - 236 years ago, America achieved independence and 236 years later, the Shifang people are fighting for their own rights and confronting the government," a microblogger wrote. "The government has repeatedly squandered the people's patience. It is time for us to be independent." AGENCIES