Demonstrators hurled chunks of concrete at police, who responded by filling a picturesque Paris square with tear gas Thursday as protest marches over a contested jobs law erupted into violence.
Prime Minister Dominique de Villepin and union leaders, meanwhile, agreed to meet for the first time in the standoff.
The five main unions accepted an invitation from Villepin to meet on Friday but said they would only restate their position and would not negotiate unless he withdraws the law. Unions plan a national strike on Tuesday.
Villepin agreed to meet with the unions despite their uncompromising stance, signaling a possible softening in his rigid stance as the government faces escalating protests that have wreaked havoc at universities, many shut down by strikes
The clashes between youths and police were reminiscent of the riots that tore through France's suburbs last fall and shook up the country. Those riots were blamed in part on youth unemployment — which the government says the new jobs law is aimed at reducing.
Violence erupted in several cities Thursday as at least 220,000 students and other youths marched nationwide. France's largest union of high school students, FIDL, estimated that 450,000 participated.
Tensions heated up on Paris' verdant Esplanade des Invalides, with riot police using tear gas on rowdy protesters who threw grapefruit-sized chunks of concrete at police officers. Some of the 23,000 marchers turned on each other, beating and kicking.
Plumes of smoke billowed skyward as youths set trash bins on fire, and vandals smashed glass bus shelters and windows at several shops. A phalanx of hundreds of riot police, three men deep, pressed forward to drive back the protesters and blocked off the ornate Alexandre III bridge.
In Paris, dozens of demonstrators appeared injured — several with blood streaming down their faces. Police said 420 people were arrested nationwide, and 18 officers were injured.
The tensions seemed to be subsiding as night fell.
"The movement is destroying itself, we've turned upon each other," Gael Ojardias, a 25-year-old cook at the Paris march, said after watching demonstrators turn on a fellow marcher and beat him.
In Lyon, students smashed store windows stores along the march route and disrupted traffic on two major highways. Police used tear gas on protesters in Grenoble, where an officer was injured, and groups of youths clashed with police in Marseille.
A radical fringe emerged at the start of the Paris march, jumping on cars and breaking shop windows. Several journalists and others were roughed up by protesters. At least 30 cars had their hoods crushed in and windshields broken.
The jobs law, meant to put the brakes on sky-high unemployment among youths and make France's economy more flexible, would allow employers to more easily hire — and fire — workers under 26. Critics feel it will eat into job protections and leave youths even more vulnerable.
"This is our big chance as a generation, because we're all united. Me alone, I can't do anything, but all of us together are going to achieve our goal," said Ivan Dion, a 17-year-old high school student at the Paris march.
Fallout from the jobs law, passed by parliament this month and expected to take effect in April, has shaken students and government alike. It could take a toll on the governing conservatives, including Villepin, both top would-be contenders for the presidential elections next year.
By Thursday, 21 universities were on strike to protest the jobs law with disturbances at 46 others, the Education Ministry said. The protest movement also was disrupting high schools.
Villepin has said he is ready to discuss modifying the most criticized aspects of the measure: the two-year period during which an employee can be fire and justification for the firing. Currently, none is needed.
In a joint communique, the unions reiterated their demand that the government withdraw the law before they would "engage in any dialogue or negotiations on jobs, insecurity or the future of youth."
Students were deciding whether to accept an invitation for a meeting with Education Minister Gilles de Robien on Friday night, though they, too, insisted that they would not negotiate terms of the law until it is withdrawn.