French police clashed with stone-throwing protesters as tens of thousands of people started marching in Paris Wednesday for May Day rallies under tight security. More than 200 arrests were made, reports AP.

Riot police repeatedly used tear gas and sting grenades to try to control the crowd gathering near Paris’ Montparnasse train station for the main protest. It wasn’t immediately clear how many people were injured. At least two men with head wounds were helped away from the scene by paramedics.

Some threw rocks and other objects at police officers, attacked a parked van in a nearby street, kicking the vehicle and breaking its windows.

Paris police said 55 people were arrested in the Montparnasse area, out of a total of more than 200 arrests on May Day. Officers also carried out more than 12,500 “preventive searches” of bags.

French authorities have warned “radical activists” may join the Paris demonstration and renew scenes of violence that marked previous yellow vest protests and May Day demonstrations in the past two years.

French police ordered the closure of more than 580 shops, restaurants and cafes on the Paris protest route and numerous subway stations were shut.