More than a thousand people gathered in the eastern Chinese port city of Ningbo on Saturday to protest against plans to expand a petrochemical plant, highlighting a major challenge for the leadership as it readies for its once-in-a-decade power transition.
On Friday, protesters overturned a police car and attacked the police.
By early Saturday, protesters, watched over by police, gathered in a central shopping street in Ningbo, wearing masks and giving out pamphlets denouncing the expansion of the plant by a subsidiary of China Petroleum and Chemical Corporation in the district of Zhenhai.
"PX...Get out of Ningbo!" read one placard, in a reference to the chemical paraxylene, which the protesters said was a carcinogen.
The protests come just two weeks before the Communist Party holds a congress which opens on Nov. 8 and will unveil the country's new central leadership.
The past few years has seen a rise in protests over environmental issues. In July, Chinese officials cancelled an industrial waste pipeline project after anti-pollution demonstrators occupied a government office in eastern China.
These protests, which are tolerated more than those driven by political concerns, pose a conundrum for the authorities which want to maintain social stability but also present an image of listening to the needs of ordinary people.
On Weibo, China's version of Twitter, discussion of the protests was not blocked but some users in Ningbo reported difficulty in uploading photographs.
The Ningbo Municipal Public Security Bureau Zhenhai branch released a statement urging protesters to express their demands in a lawful manner.