Tensions came to a head during national protests in France on Tuesday as masked rioters, angry with a government proposal to raise the retirement age from 60 to 62, lit fires and clashed with police across the country.

Hundreds of thousands of people took to the streets during the sixth nationwide day of protests since early September, spurring long lines at gas stations and disruptions in train and air travel in the economically troubled European country.

President Nicolas Sarkozy says the retirement reform must pass to salvage France's pension system, which is losing money and contributing to the country's massive deficit.

He also promised to crack down on "troublemakers" and to restore public order, leading to speculation that more confrontations with rioters are yet to come.

Union leaders have pledged to keep up the protests until the government abandons the controversial proposal, arguing that retirement at age 60 is a basic social right.

More than 200 demonstrations were planned across the country Tuesday. At some, students clashed with police. Workers continued to blockade oil refineries, leaving 4,000 gas stations without fuel, the country's environment minister said, and forcing some airlines to re-route flights in order to fuel up.

In the Paris suburb of Nanterre, a few hundred teenagers threw stones at crowds of police, who tear gassed and then barricaded the area. Similar clashes erupted at protests elsewhere in the capital.

"They have a huge attachment to their social benefits," CTV's Omar Sachedina reported Tuesday from Paris. "This is a very contentious issue."

"Protests are nothing new in France -- it's almost a French way of life," he added. "But in this situation, it's really the size and the scope of the protests."

Pension change

The proposal to raise the retirement age was announced as nations throughout Europe slash spending and raise taxes in an attempt to recover from the global recession.

Sarkozy says the country's pension system is losing money as the French live longer and longer, and that delaying retirement until 62 would still leave France with one of the lowest retirement ages in Europe.

"This reform is essential, France is committed to it, and France will carry it out," Sarkozy said Monday in the Normandy beach resort of Deauville.

However, much of the country's labour force feels the move could be the first step in whittling down France's social safety net, which features lengthy vacations, contracts that discourage employers from laying off workers, and public health care.

"It's important to come out because France wouldn't be what it is today if the generations that came before us hadn't taken to the streets," Lidwine Mure, a teacher at a protest in Paris, told the Associated Press.

The bill is expected to pass a vote in the Senate this week. Originally slated to take place on Wednesday, it's been postponed to Thursday so lawmakers can consider hundreds of amendments proposed by the opposition.

Travel disruptions

Meanwhile the protests, which were largely peaceful until Tuesday, have significantly curtailed travel in and out of France, particularly domestic flights or trips within Europe, as air traffic controllers join the demonstrations.

The Paris airport authority warned travellers to expect "serious difficulties" in accessing airports and air traffic. France's DGAC civil aviation authority said up to half of flights Tuesday out of Paris's Orly airport would be cancelled, as well as 30 per cent of flights out of other French airports, including Charles de Gaulle.

Truckers bogged down highways by driving slowly in protest. Some blocked an oil depot in the Paris suburb of Nanterre Tuesday, preventing other truckers from filling up on gasoline.

Students joined in last week, blockading high schools around the country and staging demonstrations that led to a few clashes with police. On Tuesday, 379 high schools across France were blocked or disrupted, the highest number so far in the student mobilization against the bill, according to the Education Ministry.

In the port city of Marseille, union support remained high despite garbage strikes that have left sidewalks covered in piles of trash.

"Transport, the rubbish, the nurses, the teachers, the workers, the white collar, everyone who works, we should all be united. If there is no transport today, we're not all going to die from it," 55-year-old resident Francoise Michelle told The Associated Press.

With files from The Associated Press