BEIJING (AP) — Chinese authorities say they have detained 18 people after a protest against a planned chemical plant in a southern city turned violent.

Police in Maoming city announced Thursday the suspects were accused of disrupting order and causing trouble, according to the Communist Party newspaper People’s Daily.

More than 1,000 people gathered in front of the city’s Communist Party offices on Sunday to protest plans to build a plant to manufacture paraxylene, a chemical used in the production of plastic bottles and polyesters. Similar plants have been opposed in several cities across China because of health concerns.

The protest was initially peaceful but turned violent after police reinforcements arrived and tear gas was fired to disperse the demonstrators. A number of people were injured.