Police are hunting for violent protesters after people took to the street against a waste incineration project in Hangzhou.
At a news conference on Sunday, Bian Weiyue, deputy police chief of the Zhejiang provincial capital, said protesters who damaged public and private property, including turning several police cars upside down, injuring auxiliary police and blocking expressways, must turn themselves in.
Two suspects have already done so, Bian said.
A video released by the government showed protesters beating police officers and hurling objects at broken police vehicles, one of which was on fire.
The incineration plant is planned for Hangzhou's suburban Yuhang district, 17 kilometers north of the city centre, with a designed daily capacity of 3,000 metric tons of waste.
Residents took to the streets last week after speculations that "the government started sending trucks in for construction", said a man surnamed Ma who lives 6 kilometers from the project.
On Friday, the government said that "the project won't proceed" unless legal procedures are followed and an agreement reached.
Ma said protests stopped on Sunday as the government sent thousands of police, who cordoned off villages near the project.
"You can see police officers at every street corner within a kilometer radius of the project," Ma said.
Waste incineration plants have caused many protests around China in past years because the public is nervous about possible health and environmental hazards.
Chen Liwen, a member of Nature University, a non-government environmental protection organisation, said the government should have communicated more adequately with residents before taking any action on the project.
"A lack of communication is the main reason for the Saturday clash," she said.
Chen said that waste incineration plants, even operating under the highest of environment standards, will have negative health effects on nearby residents.
But Zhang Yi, head of the Shanghai Environmental Sanitation Engineering Design Institute, said that the fear of dioxin, a carcinogen that is the main health hazard from waste incineration, played a part in fanning protests.
"It's not as bad as some reports said. Under strict emission controls, a plant would have to operate tens of thousands of years for the level of dioxin to cause any harm to the human body," he said.