Authorities in the city of Ningbo in eastern China agreed today to halt a planned factory expansion after days of protests.
Demonstrations began on Friday over fears that plans to increase the plant's oil-refining capacity by 15 million tons and its ethylene production by 1.2 million tons would worsen air pollution.
The factory makes paraxylene, which is used in the manufacture of plastic bottles and fibres but poses serious health risks if not handled properly.
Marchers gathered in the central Tianyi square in their highest numbers yet today morning and marched to the municipal government headquarters, which were guarded by riot police.
At least three people were arrested, apparently after scuffles with officers, and some threw bottles after police tore their posters from railings and trees.
Protester Yu Yibing said: "We need to live in a green environment. This is a reasonable request. I don't know how else we can express our views."
Many marchers recorded events on smartphones and tablet computers and some brought their pet poodles on the demo.
Authorities had maintained that the proposed expansion met "stringent" safety and environmental standards and had not been approved yet anyway.
At talks with residents on Saturday evening Ningbo Communist Party secretary Wang Huizhong and Mayor Liu Qi had pledged a further environmental assessment and said they would only proceed in consultation with the local population.
But it was not enough and after today's protests municipal authorities said that the expansion would no longer go ahead as it clearly lacked popular support.