The large protest highlighted Chinese citizens' increasing boldness in demanding action from the authoritarian government, particularly on environmental issues, even though the government rarely gives in.

More than 100 police officers including about a dozen riot police patrolled the public square in front of government offices in the northeastern port city of Dalian, where more than 12,000 people had demonstrated over pollution concerns.

Soon after Sunday's protest, censors had begun removing information about it from microblogging sites.

There was no sign that people were gathering to protest for a second day after Dalian officials pledged Sunday, in what appeared to be a rapid response, to move the Fujia chemical plant out of the city and ordered its immediate shutdown.

The move came after scuffles broke out earlier in the day between riot police and more than 12,000 protesters demanding that the plant, which produces the chemical paraxylene, or PX, be moved after a tropical storm raised fears of a toxic spill, state-run Xinhua News Agency said. No injuries were reported in the confrontations.

Calls to relocate the plant grew after waves from Tropical Storm Muifa broke a dike guarding it last week and raised fears that flood waters could release toxic chemicals. There was no actual chemical leak, Xinhua said.

Paraxylene is widely used in the production of polyester. Short-term exposure can cause eye, nose or throat irritation in humans, and chronic exposure can affect the central nervous system and cause death.

Despite the apparent success of the protest, censors quickly began deleting references to it on social networking sites -- a usual practice to prevent demonstrations from spreading.

A video posted on the microblogging site Weibo showed the city's top official, Tang Jun, standing on a police van trying to appease the crowd. Xinhua said Tang and Mayor Li Wancai promised to move the plant out of the city, but some protesters refused to budge until a timetable was given.

A statement posted on the website of the State Council, China's Cabinet, on Monday said the Dalian Communist Party and city government decided Sunday to "stop the Dalian PX project immediately and relocate the plant." The statement had been taken down one hour later.

Although the government rarely gives in, a similar environmental protest four years ago was successful.

In that case, plans for a paraxylene plant in the city of Xiamen in southeastern China provoked protests in 2007 from residents worried about health hazards. In 2009, the Environment Ministry said it would be built instead in a less populated area of another southeastern city, Zhangzhou.

On Friday, the Zhangzhou government said a paraxylene plant there is expected to be completed there by the end of this year and will start operating early next year.