Four officers and 12 demonstrators were injured in the clashes in the capital, and police made 59 arrests.

According to the interior ministry, half a million people participated in largely peaceful protests in several French cities. But as darkness fell on the Place de la Nation, the finishing point for the demonstration in eastern Paris, rioters stormed a McDonald’s restaurant, smashed telephone booths and threw projectiles at police.

Several hundred protesters had lingered after the demonstration, massing in the centre and around the edge of the square. Riot police, backed by vans fitted with protective shields, fired tear gas to clear them, beating their shields with batons as they charged from avenues and narrow streets into the square.

Some demonstrators said the rioting youths had appeared only at the end of the protest, which had been staged against a new law making it easier for employers to sack young workers. But Suzanne Dufoix, 20, a philosophy student, blamed the police for the violence.

“This is all the police’s fault,” she said. “Who asked them to charge us when we were just listening to music and the demo wasn’t even over yet? Lots of the people chucking things at the cops are students like me, they are sick of uncertainty, and this is a chance to make ourselves heard.”

Sébastien Lasau, 26, a railway worker, confirmed that many of the rioters were students. “They are daddy’s boys from the chic arrondissements. They came equipped with scarves and lemons to counter the effects of the tear gas, and many of them have ski goggles as well.”

Earlier, the demonstrators in Paris had marched under a clear, blue sky, chanting “No to the Kleenex contract”, arguing that the law, known as the first job contract, would allow employers to discard workers like used tissue paper.

“We will not be the bosses’ fodder,” said Vincent Martin, a 25-year-old student from the Sorbonne. “We will continue to protest until the government withdraws this unjust law.”

Anticipating violence, the police had removed from the marchers’ path rubbish bins and scaffolding, potential weapons in the hands of youths who had destroyed cars and set fire to a famous bookshop in a protest on Thursday.

The government had been extremely nervous about the prospect of a repeat of the disorder that set Paris and several other big cities ablaze late last year when thousands of cars and hundreds of buildings were burnt by youths from immigrant suburbs.

Although they seemed to fall short of the crowd of 1.5m that organisers had expected, yesterday’s protests were described as a “black Saturday” for Dominique de Villepin, the beleaguered centre-right prime minister, whose difficulty in winning support for his employment law has worked against his dream of succeeding President Jacques Chirac after the election in May next year.

Students have closed 16 universities and disrupted classes at 35 others in protest at the law, which is intended to encourage hiring in companies wary of taking on new staff. Chirac called for negotiations on the law but stood by it, calling it “an important element in the policy of fighting unemployment”.

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