French students set fire to bins and erected blockades outside schools in several cities on Thursday, protesting overcrowded classrooms, teacher shortages and crumbling facilities.

Several school principals were injured, harassed or assaulted during blockades at high schools on Thursday, according to reports from regional education authorities, prefectures and union representatives.

Police have already detained hundreds of protesters at the lycees, which students aged 15 to 18 attend for their final three years of secondary education in France.

The government said the demonstrations had become "urban violence." Prime Minister Sebastien Lecornu on Thursday urged all ministers to postpone any travel nationwide, said a source close to the minister.

This latest wave of social unrest comes just seven months away from France's presidential election, where opinion polls put far-right leader Marine Le Pen as the frontrunner and with tensions already running high over inflation, particularly soaring fuel prices.

A security source said there had been 900 blockades or related incidents across the country on Thursday.

More than 160 schools were shut down, and university students joined the protests in Paris, Marseille and other cities.

Since last week, pupils have staged protests outside schools over a range of grievances. They range from timetables, class sizes and a shortage of teachers to overheated classrooms during this year's heatwaves.

The protests have spread across the country from the Paris suburbs, and the government has accused hard-left politicians of encouraging the unrest.

Riot police have lined up against the students, and the force has launched internal probes after accusations of brutality against three pupils, said Interior Minister Laurent Nunez.

University students also joined in, blocking access to around 30 campuses, a student union said.

In the northwestern city of Nantes, firefighters had to intervene to extinguish a fire in the entrance of a high school "following a gathering marked by violence towards staff," the regional education board said.

Authorities reported violence near high schools, mainly in Nantes, blaming "violent individuals" who "join the students to carry out acts of vandalism."

In the northeastern city of Strasbourg, trams were ordered to grind to a halt to "restrict the movements of rioters and demonstrators," the regional prefect said.

Raphael, a 17-year-old who did not give his surname for fear of reprisals, was among the protesters outside a school in Strasbourg, where some used barriers to obstruct the nearby tramway tracks.

"There are 35 of us per classroom. With 35C in summer, it's unbearable. There aren't enough toilets, and there are water leaks in some rooms," Raphael said.

"The building is falling apart, the cafeteria is too small. There's zero budget, zero resources, not enough supervisors," he said.

Nearby, students took photos of themselves in front of burning rubbish bins, holding up the sign with their school's name ripped off the tram stop.

Most pupils did not take part in any vandalism, instead breaking into a sprint down an avenue when the police fired tear gas.

In the southern city of Toulouse, hundreds of young people flooded the tram tracks, some toppling trash cans and starting fires, hurling projectiles or smashing bus shelters.

In the northern city of Lille, reporters saw young people wearing black hoodies destroy the glass of a bus stop. Firefighters intervened to put out the flames on upturned dustbins set on fire.

The government has accused the hard-left France Unbowed (LFI) party of encouraging the protests.

But LFI's candidate for the 2027 presidential election, Jean-Luc Melenchon, said on Wednesday that his party "called for non-violent methods of struggle."

In neighbouring Belgium, there were protests and damage at a handful of schools in the eastern city of Liege, police said. (AFP)



Edited by Cecil Wong