NINGBO: Protests resumed Sunday in an eastern Chinese city where thousands of residents had clashed with police a day earlier while demonstrating against the proposed expansion of a petrochemical factory over pollution fears.    

Several hundred citizens of Ningbo, which is in Zhejiang province, set off from a city square and headed for the offices of the municipal government on Sunday morning. Hundreds were stopped at the gate of the offices by a circle of uniformed police. They shouted for the release of people they believed had been detained by police a day earlier, for the protection of Ningbo and for the city's mayor to come out.

''We can only depend on ourselves now, we can't count on the government to think about us,'' said one protester, a 40-year-old woman surnamed Jing.

On Saturday, residents reported that protests involved thousands of people and turned violent after authorities used tear gas and arrested participants. Authorities said ''a few'' people disrupted public order by staging sit-ins, unfurling banners, distributing fliers and obstructing roads. Authorities said that the proposed project was under evaluation and that the public was being given opportunities to offer its input.

There have been a series of protests in China this year over fears of health risks from industrial projects, as members of the rising middle class become more outspoken against environmentally risky projects in their areas.    A week earlier, hundreds protested for several days in a small town on China's Hainan island over a coal-fired power plant.

Such protests are exactly what the Chinese leadership does not want ahead of next month's once-a-decade transition of power, with stability being paramount.

The demonstrations are a reminder to the incoming generation of leaders that they face a public increasingly unwilling to accept the environmental and health hazards as an inevitable consequence of breakneck, unbridled economic growth.

A 30-year-old woman surnamed Wang said officers took her to a police station Saturday and made her sign a guarantee that she would not participate in any more protests, but she came back Sunday anyway.

''They won't even let us sing the national anthem,'' Wang said. ''They kept asking me who the leader of the protests was and I said that this is all voluntary. We have no leader.''

Marchers included the elderly and children, as well as some pet poodles. People held up smartphones and tablet computers recording the protest and tried to send information to others through mobile Internet connections.

In a sign that censors were at work, the name ''Zhenhai'', the city district where the factory is located, was blocked on China's popular microblogging site Sina Weibo and searches for ''chemical expansion project'' were greeted with the line that ''Some search results are not shown according to regulations.''

Those that were visible included postings from media sites that said authorities were holding meetings to hear public opinion.

Some protesters wore face masks and shouted slogans including ''Protect Ningbo'' and ''Return my health'' while pumping their fists in the air. Cars were forced to stop as a long stretch of people marched along roads.

''We have to do this for our future and our family's future,'' said protester Jing as she pointed to the smoggy air. ''The sky was so clear when I was a child. Look at it now.''

Another protester, Yu Yibing, said he wanted the factory to be closed, not expanded, and his 7-year-old son to grow up in a clean environment.

''As the common people, we need to live in a green environment. This is a reasonable request,'' said Yu, 38. ''But the government only puts out some statement and refuses to see us and also suppresses us. I don't know how else we can express our views.''

The Zhenhai district government, which comes under the Ningbo government, said Ningbo's Communist Party chief, Wang Huizhong, and mayor, Liu Qi, had held discussions with local residents Saturday night.

A statement posted on the district government's website Sunday said that the opinions and advice of the people who attended ''are very helpful'' to the party committee and municipal government's decision-making and that the expansion project was ''at an early stage.''

''We will further solicit opinions and respond to people's concerns and actively respond to people's reasonable requests and demands,'' the statement said.

The Zhenhai government earlier said it would organize public hearings attended by residents and experts to assess the environmental impact of the project.

The official Xinhua News Agency said the planned project is designed to produce 15 million tons of refined oil and 1.2 million tons of ethylene per year and belongs to Sinopec Zhenhai Refining & Chemical Company, which has invested $8.9 billion.

Calls to Zhenhai police and the propaganda department of Ningbo police rang unanswered Sunday.