Gangs of masked youths smashed windows and hurled stones at riot police as thousands of people marched through Paris on Tuesday in protest at a planned change of labour laws that would make hiring and firing easier, reports Reuters.
Police fired dozens of volleys of teargas and used water cannon to disperse highly mobile groups of mostly black-clad youths. The police department reported 13 arrests in the early stages of a street march led by labor unions.
After violent clashes between riot police and masked youths during previous demonstrations, Paris police had feared further incidents and banned 130 would-be troublemakers before Tuesday's rally even began.
It was not immediately clear which group, if any, the youths belonged to. The government and police have condemned what they say are groups of ultra-violent youths who join protests looking for a fight.
Tuesday's march comes at a time when police are stretched to ensure security during the month-long Euro 2016 soccer tournament, with France on maximum alert since Islamist militants killed 130 people in Paris in November.
The CGT labour union said the march would be the biggest show of strength since protests over the planned labour reform began in early March.
"This is not the end," CGT leader Philippe Martinez said. "The struggle is far from over."
The CGT, backed by smaller unions in a campaign of strikes and protests, is sparring for pole position with another big union that backs the reform that would also devolve setting of pay and working conditions more extensively to company level.
About 700 buses ferried protesters to the capital from all over France for the march, Martinez said. Smaller protests were being staged in other cities.
Police planning was based on the possibility that more than 50,000 - twice previous levels - would take part, Paris Police Prefect Michel Cadot told a pre-rally news conference.
On many previous occasions, gangs of what the government and police have described as ultra-violent youths have engaged in running battles with law enforcement officers, ransacking shopfronts and street furniture.
In tandem with Tuesday's protest, workers stopped work at the state-owned SNCF rail company, which nevertheless said disruption was far less than at the outset of a rolling strike two weeks ago or on previous occasions this year.
Ninety percent of high-speed connections were operating and other services were working at about 70 percent, the SNCF said.
The CGT union and smaller Force Ouvrière union argue that the reform will undermine standards of labour protection.
The government, and the large CFDT union argue the contrary, saying it will help tackle a jobless rate of 10 percent and also develop labour representation at grassroots level. Youth unemployment is about 24 percent.