The eastern Chinese city of Ningbo has cancelled plans to expand a petrochemical complex following a week of sometimes-violent protests sparked by concerns over the environmental impact, state media has reported.

A spokesman for Ningbo city government said in a statement carried by the official China News Service that no further work would be carried out on the project in Zhenhai district pending further "scientific debate".

Protests in the eastern city, had swelled over the weekend and led to clashes between citizens and police. The Ningbo city government said in a statement on Sunday evening that they and the project's investor had "resolutely" agreed not to go ahead with the expansion.

The factory is a subsidiary of Sinopec, one of world's the biggest petrochemical companies.

Outside government offices an official tried to read the statement on a loudspeaker but was drowned out by protesters demanding the resignation of the mayor and the release of demonstrators being held inside.

Liu Li, 24, a Ningbo resident, said the crowd did not believe the government's statement. "There is very little public confidence in the government," she said. "Who knows if they are saying this just to make us leave and then keep on doing the project?"

The city government was likely to be under pressure to defuse the protest with China's leadership wanting calm for next month's party congress. It was unclear whether local authorities will ultimately cancel the petrochemical project or continue it when the pressure is lower.

Hundreds of people outside the government offices refused to disperse despite being urged to leave by officials. Riot police with helmets and shields pushed the crowd back. Six men and one woman were dragged into the compound by police, who beat and kicked at least three of them. Police also smashed placards and took away flags.The demonstration in wealthy Zhejiang province is the latest this year over fears of health risks from industrial projects, as Chinese who have become more outspoken against environmentally risky projects in their areas despite improvements in their living standards.

"The government hides information from the people. They are only interested in scoring political points and making money," said one protester, Luo Luan. "They don't care about destroying the environment or damaging people's lives."

The protests began a few days earlier in the coastal district of Zhenhai, where the petrochemical factory is located. On Saturday, they swelled and spread to the centreof Ningbo city, whose officials oversee Zhenhai.

Residents reported that Saturday's protests involved thousands of people and turned violent after authorities used tear gas and arrested participants.

Authorities said "a few" people had disrupted public order by staging sit-ins, unfurling banners, distributing fliers and obstructing roads.