Thousands of people in an eastern Chinese city clashed with police while protesting the proposed expansion of a petrochemical factory that they say would spew pollution and damage public health, townspeople said Saturday, Oct 27, according to The Associated Press.

Pollution has become a major source of unrest in China, as members of the rising middle class become more outspoken against environmentally risky projects in their backyards.

The Zhenhai district government in Zhejiang province's Ningbo city said in a statement Saturday that "a few" people disrupted public order by staging sit-ins, unfurling banners, distributing fliers and obstructing roads. It said the proposed project was under review.

Zhenhai police said protesters threw rocks and bricks at officers Friday and that police dispersed illegal gatherings to restore the flow of traffic.

Residents, however, said the protests involved thousands of people and turned violent after authorities used tear gas to dispel the crowds and arrested participants.

Photos posted online showed demonstrators clashing with police and holding up signs demanding that the project be halted.

Searches for phrases including Zhenhai and Zhenhai chemical plant were blocked Saturday on the microblogging site Sina Weibo.