Demonstrations against French President Emmanuel Macron's pension reform are drawing more and more radical protesters, with up to one in five voters approving the use of violence to further the cause, according to polls.

Since January, weekly demonstrations organised by trade unions have drawn millions of people nationwide, with the marches remarkable for both their scale and their overwhelmingly peaceful nature.

But last Thursday's demonstrations appeared to mark a turning point, with more than 400 security forces injured and hundreds of fires lit in the streets of Paris.

Further clashes took place on Tuesday in the capital, as well as in other towns including Nantes in western France, with hundreds of anarchists spotted in the crowds alongside outraged voters.

"I don't think peaceful demonstrations are enough " Jerome, a 49-year-old French civil servant told AFP on Tuesday as he joined the demonstration in Paris, asking for his surname to be withheld because he worked for the state. "If there's no violence, people don't talk about it.

"A few smashed windows, who cares? They won't go to hospital," he added.

His friend and fellow civil servant Ludovic, 48, agreed that violence could be a legitimate last resort, including against the police.

"It's understandable. It's exasperation," he said. "After being ignored for so long, if that's only thing left to use, then that's the way it is."

A poll by Toluna Harris Interactive on Tuesday suggested that one in five respondents (18 percent) "approved" of violent means to further the goals of the movement.

Among people who said they backed the protests, the figure rose to 25 percent.

- 'Yellow Vests' redux? -

The clashes have sparked a debate about whether the scenes of smashed windows, tear gas and fires -- carried live by French and international news channels -- help opponents to Macron's reform, or distract from the cause.

Only four years after the anti-government "Yellow Vest" protests shook the country, some fear a repeat of the weekly clashes that left 11 dead, 2,500 protesters injured and 1,800 police hurt.

After a weekend protest against a reservoir in southwest France left two protesters in hospital, the France 5 news channel held a debate on Monday evening titled "Violence: is our democracy sick?"

"The violence is not the issue here," argued Helene Gardes, a 29-year-old special needs teacher, at the demonstration on Tuesday. "Most people in the country are against this reform. They come and march peacefully, so focusing on the violence is missing the point."

Trade unions have called for the strikes and protests to continue while also condemning the so-called "casseurs" (vandals) responsable for clashing with police and damaging property such as shops, cars and banks.

"I'm worried about it," Laurent Berger, the head of the moderate CFDT union, told reporters on Wednesday when asked about the risk of clashes. "You'd have to be reckless to not worry about it."

Macron remains defiant and is on the verge of pushing through a rise in the retirement age from 62 to 64 having used a notorious constitutional power to pass the legislation without a vote in the National Assembly.

French security services had warned that the protest movement could turn more radical.

Many young people at the demonstration on Tuesday said they had decided to protest because of what they saw as Macron's contempt for democracy and public opinion, which is overwhelmingly against the reform.

"In France, we had the Revolution," Maxime Peraut, a 22-year-old postman and musician, told AFP, referring to the famed 1789 uprising against rule by the Bourbon royal family.

"I think we need to do something similar to move on to something new and start again on better foundations."