Violence has erupted in Paris and other cities as tens of thousands of French students took to the streets to protest against a controversial labour law.
Paris police tried to separate peaceful protesters and rioters
Dozens of youths smashed windows, looted shops, set fire to cars and hurled stones at police.
About 420 people were arrested, police said, and dozens were injured. Tensions were said to have eased by nightfall.
Union leaders have agreed to meet Prime Minister Dominique de Villepin on Friday. They want the law withdrawn.
The union leaders have refused to negotiate unless the law, introducing the First Employment Contract, is withdrawn first and will only use the meeting to press their demands. A strike is due to be held on Tuesday.
Mr de Villepin has said he will talk about amending but not scrapping the law, which is an attempt to create jobs for the young by dropping employment safeguards.
The BBC's Caroline Wyatt in Paris says the prime minister is becoming increasingly isolated in his desire to push through the contract.
Protests have spread across France in recent weeks, and several of them have ended in violence.
Government officials said at least 220,000 people took part on Thursday, many of them high school or university students, although organisers put the figure at 450,000.
In central Paris, clashes with police were brief and involved only a few hundred youths at most, some of whom appeared not to have been part of the march.
They threw stones at the police who stood ready with their riot shields as they blocked off two bridges along the Seine.
Some shop windows were smashed and one shop was set on fire too. Around 140 people were arrested.
The majority of protesters were peaceful, many of them linking arms as police tackled the violent fringe.
Many protesters sought to distance themselves from the violence.
Mr de Villepin is under pressure to negotiate over the law
"This time, there are lots of young criminals on the march who are there to steal and smash. This discredits the movement," 22-year-old worker Charlie Herblin told Reuters news agency.
During the protests, violence also broke out in suburbs of Paris, in Marseilles, Lyon, Grenoble in the south-east and in the western city of Rennes.
Sixty people were injured nationwide, 27 of them police.
Job stability fears
Correspondents say Mr de Villepin is coming under pressure from President Jacques Chirac to negotiate over the law, which could damage his own hopes of becoming president.
His government proposed the law as part of a series of measures designed to help youths in the French suburbs who took to the streets last year.
The law allows employers to end job contracts for under-26s at any time during a two-year trial period without having to offer an explanation or give prior warning.
The government says it will encourage employers to hire young people but students fear it will erode job stability in a country where more than 20% of 18 to 25-year-olds are unemployed - more than twice the national average.