Violence flared in Paris and other French cities on Thursday as at least 170,000 workers and students made a new push for the withdrawal of a hotly contested labour bill.

Security forces in the French capital responded with teargas as masked youths threw bottles and cobblestones at security forces, leaving three policemen with serious injuries, Interior Minister Bernard Cazeneuve said, adding that 24 police were injured overall.

Clashes between police and protesters also erupted in the cities of Nantes, Lyon, Marseille and Toulouse, with 124 people arrested nationwide, Cazeneuve said in Lyon.

He called on organisers to "condemn these excesses by a handful of hooligans with the same firmness as my own."

The demonstrations as well as work stoppages, notably in the aviation and public transport sectors, were the latest actions in a protest wave that began two months ago.

Opponents of the reform, billed as an effort to reduce chronic unemployment -- which stands at 10 percent overall -- say it will threaten cherished workers' rights and deepen job insecurity for young people.

"Be Young and Shut Up!" read one banner at a protest in southwestern Toulouse, highlighting the frustration of youths facing an unemployment rate of 25 percent.

"Over the past 10 years or so things have deteriorated horribly for young people," said retiree Gilles Cavaliere at the Lyon protest.

Also Thursday, striking aviation workers caused one in five flights to be cancelled at Paris's Orly airport, while delays were reported at Charles de Gaulle airport.

And newsstands were devoid of national dailies after printers downed tools.

The unions and student organisations plan to pile on the pressure with further protests on Sunday to mark the May Day labour holiday, as well as next Tuesday, when parliament begins debating the bill.

Christophe Sirugue, the Socialist lawmaker who is presenting the bill to parliament after it was reviewed in committee, said Thursday that several points still needed "clarification" but that he expected the bill to pass.

Among the remaining issues are measures to make it easier to lay off workers in lean times, and whether employers should still be allowed to shed workers if conditions are depressed in their overseas operations and not just in France.

Another is a proposed surtax on short-term contracts aimed at getting employers to hire more people on permanent contracts, Sirugue told reporters.

Young people have been at the forefront of the protest movement, with many young workers stuck on short-term contracts or internships while hoping to secure a permanent job.

Protests against the reform kicked off on March 9, culminating in massive demonstrations on March 31 that brought 390,000 people on to the streets, according to an official count. Organisers put the number at 1.2 million.

The CGT union said Thursday's marches and rallies drew half a million people.

The protests spawned a new youth-led movement called "Nuit Debout" (Up All Night), which has seen advocates of a broad spectrum of causes gather in city squares at night for the past four weeks to demand change, though attendance has been dwindling in recent days.

With little more than a year left in his mandate, France's deeply unpopular President Francois Hollande has been banking on the labour reform as a standout initiative with which to defend his record.

But in the face of the protests his Socialist government has watered down the labour reforms -- only to anger bosses while failing to assuage workers.

"The current bill, which is totally unacceptable, spells insecurity and social setbacks for workers and youths," a joint union statement said.