The protest was triggered by mounting fears over the safety of a factory that makes paraxylene—a flammable carcinogenic liquid used in the production of polyester films and fabrics—which belongs to the Fujia Group.

On Monday, residents living near the plant had to be evacuated after waves triggered by an incoming storm breached a dyke protecting the factory and threatened to damage the building, sparking fears of a toxic chemical spill.

Workers managed to repair the dyke, but residents have been left worried about the plant’s potential for environmental damage and its impact on their health.

Tang Jun, Dalian’s top official, has tried to calm the protesters, promising to move the plant out of the city, but the crowd had still not dispersed early Sunday afternoon, Xinhua said.

The Dalian municipal government was unavailable for comment when contacted by AFP.

Pictures of the protest posted on Sina’s Weibo service, the Chinese equivalent of Twitter, showed people marching down a street with a banner that read “We want to survive, we want a good environment, give me back my Dalian.”

However, AFP could not verify whether the photos were genuine.

In a sign of the sensitivity of the protest, China’s censors appeared to be stopping any mention of the subject on Sina’s Weibo.

Searches for ‘Dalian’ came up with a message saying “search results cannot be displayed due to relevant laws, regulations and policies.”

Pollution-related scares are common in China — the world’s biggest emitter of greenhouse gases — where an emphasis on economic growth over the past three decades has led to widespread environmental degradation.

As such, environmental problems have triggered a rising number of riots and other forms of public unrest over the years.

In one high-profile case in 2007, work on a billion-dollar petrochemical plant in the south-eastern port city of Xiamen was scrapped following huge public discontent about industrial pollution.