PARIS • Several dozen youth protesters clashed with police in the early hours yesterday in a central Paris square after refusing orders to disperse, French police said.

Officers detained 24 people overnight after scenes of violence that saw protesters hurling chunks of concrete at riot police and torching vehicles. About 100 "especially violent demonstrators" forced their way through a police barricade at the Place de la Republique, the police said.

The square has been the venue for the past month of nightly gatherings dubbed "Up All Night" but, on Thursday, protesters - numbering around 1,000 - were allowed to stay only until midnight.

The new violence followed clashes on Thursday during protests against France's hotly contested labour laws that left 24 policemen injured, three seriously.

At least 170,000 workers and students had taken to the streets nationwide to press demands for the withdrawal of the proposed labour law, which had been billed as an effort to reduce unemployment that stands at 10 per cent. They say it will let employers bypass regulations on basic worker rights by giving bosses greater freedom to set pay rates and working conditions.

Interior Minister Bernard Cazeneuve visited an officer at a Paris hospital on Thursday, saying he remained in serious condition. Police said he was a plainclothes officer who was hit in the head by a projectile. Speaking to reporters outside the hospital, Mr Cazeneuve praised the "great professionalism" of security forces in bringing the protests under control while "violent groups" sowed disorder.

But he rejected demands for an outright ban on demonstrations from right-wing politicians who argue that France remains under a state of emergency since the November Islamist attacks in Paris.

Trade unionist Olivier Besancenot accused the government of inviting unrest through an excessive show of force. "With this kind of deployment (of security forces) you know exactly what it will incite," he said. "You can create conditions for things to go wrong."

The protests kicked off on March 31, inspired by opposition to the proposed labour reforms, but the movement has since embraced a range of grievances and has spread to several other cities in France.

The event, which has drawn up to 3,000 mainly young people at a time in Paris, has increasingly been marred by violence, with police warning the organisers not to let their peaceful causes be hijacked by troublemakers. More than 400 people have been arrested since the demonstrations began.

AGENCE FRANCE-PRESSE