BEIJING — Several hundred people protesting the planned expansion of a petrochemical plant in the Chinese port city of Ningbo swarmed the city center for a third day Sunday, refusing to back down even after the government promised to cancel the project.
As demonstrators outside the government offices refused to disperse, riot police with helmets and shields came out of the compound and pushed the crowd back. Police dragged six men and one woman into the compound, beating and kicking at least three of them, the Associated Press reported. Police also smashed placards and took away flags.
The throng chanted slogans and demanded that the mayor step down, according to witnesses. Several protesters threw rocks and bottles at the officers.
The clashes are occurring at a delicate time for the governing Communist Party as it prepares for a once-a-decade change in leadership that is scheduled to begin Nov. 8 during a weeklong series of meetings in Beijing. Public concerns about industrial pollution have become a problem for the government, which often backs economic growth over public concerns about the environment.
Although the crowds in Ningbo were smaller than on Friday and Saturday, when thousands clashed with the police, resulting in scores of arrests and at least a dozen injuries, protesters managed Sunday to evade roadblocks and police cordons aimed at keeping people from gathering in the center.
The protesters, wearing masks and carrying banners that said ‘‘We want to survive,’’ were seeking to stop the expansion of a state-run Sinopec plant, which is already one of China’s largest refineries. The official Xinhua News Agency said the planned expansion was designed to produce 15 million tons of refined oil and 1.2 million tons of ethylene per year.
On Sunday, the government said the expansion would be canceled, but it offered few details. Protesters met the announcement with skepticism, vowing to continue the demonstrations.
Residents, citing environmental concerns, have been demanding that the government move the plant from Ningbo, a prosperous city of 3.4 million people in Zhejiang Province, near Shanghai.
In recent years, residents of China’s cities have harnessed social media to promote street protests against the construction or expansion of factories, mines, and refineries. Although such demonstrations are illegal, and the organizers face arrest, the protests sometimes have the desired effect.
In July, officials in Shifang, in the southwestern province of Sichuan, canceled plans for a copper smelter after tens of thousands of residents joined protests that turned violent.
In September 2011, a solar energy company in Jiaxing, near Shanghai, was closed after demonstrators cited noxious chemicals used in the manufacturing process. And in August of that year, officials in Dalian, in northeastern China, said a petrochemical plant would be closed and relocated after at least 12,000 people took to the streets, although the plant remains in operation.
In a statement, the Zhenhai District government condemned those it blamed for organizing sit-ins and blocking roads in Ningbo but insisted that public sentiment would be taken into consideration before any construction.
“Detailed information will be published when environmental reviews are implemented, and public opinions on the project will be heeded,’’ the statement said.
Residents have expressed concern about the refinery’s production of ethylene and paraxylene, known as PX, a toxic petrochemical used in plastics, paints, and cleaning solvents.
The demonstrations, which began last Monday when 200 farmers blocked a road near the district government’s office, according to the state news media, grew larger Friday, after student organizers were said to have issued calls through social media outlets.
Photographs of the weekend demonstrations, many taken by cellphone, appeared to show officers swinging clubs as they chased protesters or beat those who had fallen. Censors worked quickly to delete images and witnesses’ accounts that were posted on Sina Weibo, China’s popular microblogging service.
The Information Center for Human Rights and Democracy in Hong Kong said 10 people had been injured after the police fired tear gas and moved to break up the protests.
By Sunday, several Ningbo residents reported that they were unable to send photographs from cellphones or tablets. The state-run news media ignored the protests — except for a brief item in The Ningbo Daily, which declared the authorities’ commitment to seeking public opinion on the project.
In a series of online posts Saturday, Chen Yaojun, a local lawyer, described how the police had quickly tackled and dragged away protesters who dared to chant slogans. He said he had been arrested after he tried to protect a student who was being beaten by the police.
After he was dragged into a police van, Chen said, he talked to an officer who expressed regret for the rough handling of the protesters.
Yu Xiaoming, a local resident who said he had been among 12 people selected to talk to the government Sunday, said the meeting had not gone well. He said officials had frequently cut off the participants — among them several chemical engineering experts — as they tried to make their case, and warned them to be careful about what they said in public.