More than 10,000 people took to the streets in Marseille

Large crowds took part in peaceful rallies in Paris, Rennes, Marseilles, Grenoble and Nantes.

Air traffic and transport in 35 cities experienced some disturbances.

The government wants to let firms offer job contracts to people under 26 which would make it easier for them to be fired at short notice.

Speaking in parliament, Prime Minister Dominique de Villepin defended the plan, saying that France must be brave and take steps to keep moving forward in a changing world.

"For 20 years now, insecurity has been the daily reality for many young people in our country. I refuse to do nothing," he said.

Critics warn that the new legislation, which currently only applies to small firms, could be misused by larger employers and make it even harder for young people to find a permanent job.

Street marches

Several thousand teachers - between seven and 15% of the country's education workers - took part in the strike, the education ministry said.

National carrier Air France, where six unions called for work stoppages, reported several delays on short- and medium-haul flights.

Dominique de Villepin says greater flexibility will boost job opportunities

Toulouse airport experienced delays and cancellations, while public transport in Dunkerque was paralysed.

National radio stations France Info and RFI were also forced to replace most of their usual news bulletins with music.

Anenne, a protester in Paris, said: "We are students and later we want to have jobs, but we see that the situation is getting worse in France on all fronts.

"We have to come here and make ourselves heard. The vote is not enough; they approve laws without even asking us our opinion. It's not right."

Another protester said he was marching because "the precarious situation of the youth will have an impact on our retirement".

"We defend their cause and our cause at the same time."

'Boost opportunities'

The government's First Employment Contract (CPE) legislation was passed by senators on Monday but must be scrutinised by a cross-party committee before it becomes law.

The prime minister used emergency powers to push the law through the lower house last month.

The government argues the measure will boost opportunities for young workers, many of whom can only find short-term contract work at best.

After the two-year trial period, the contract would revert to a standard full-time contract.

More than 20% of France's 18 to 25-year-olds are unemployed - a figure double the national average of 9.6%.