A protest over a proposed chemical plant in a Chinese city turned violent at the weekend, officials said Monday, but added order had been restored and no-one had died.

Pictures posted on Chinese social media purported to show bloodied participants and police in riot gear in Maoming in the southern province of Guangdong.

One image on Sina Weibo, a Chinese equivalent of Twitter, showed a man lying immobile in a pool of blood.

The photos could not be independently verified for authenticity. No other postings on the incident were visible and searches returned a message that "due to relevant laws, regulations and policies" results were not displayed.

In a statement on its website, Maoming city said that citizens demonstrated on Sunday over the PX plant.

PX is an abbreviation for paraxylene, a flammable carcinogenic liquid used to make polyester films and fabrics.

Increasing environmental awareness in China has emboldened citizens to take to the streets in protest against facilities feared to be harmful to health. While authorities are sometimes tolerant, demonstrations are frequently broken up.

The Maoming city statement said the protest began in the morning with the intention of "expressing deep concern" over the proposed factory.

But in the evening small numbers of "troublemakers" threw rocks and water bottles before order was restored.

"No one died during the incident," the statement said. It did not give a figure for how many people participated or provide any details on possible injuries.