A police car has been set ablaze in Paris after an angry crowd surrounded the vehicle as tensions ran high over accusations of police brutality against protesters, police officials and witnesses said.
The police officers who were inside fled.
The incident occurred on Wednesday (local time) on a central Paris street a few hundred metres from where law enforcement officers were staging a rally to vent frustration over near daily clashes with violent gangs on the fringes of protests against labour law reform.
Witnesses and officials said the police officers were forced to abandon the car when a smoke bomb was thrown inside by people chanting "police everywhere, justice nowhere".
Hours earlier, protesters complaining of police brutality in the confrontations of recent weeks were prohibited from holding a counter-demonstration at the site where the police rally was taking place.
Wednesday's main action involved strikes by French rail and port workers which slashed train services and ferry connections to Britain as labour unions led a week of protests aimed at forcing President Francois Hollande's government into retreat.
Mr Hollande's planned reforms aim to make it easier to hire and fire people.
The government hopes they will boost employment but opponents argue they expose workers to worsening working conditions and reduced job security.
More than 300 police officers have been injured in several weeks of confrontations, mostly with violent gangs of hooded and masked rioters hurling firebombs and paving stones.