A city hall was set on fire in Bordeaux as more than a million people took to the streets across France in continuing protests against the country’s unpopular pension reforms.
Violence broke out in some areas, including at a Paris march attended by 119,000 people, a record for the capital during the upheaval.
In total, 457 people were arrested and 441 security forces members were injured during the nationwide protests on Thursday.
More than 900 fires were also lit in the streets of Paris during the most violent day of protests by far since they began in January.
Polls show most people are against changes made by President Emmanuel Macron to increase the retirement age from 62 to 64, a move he says is necessary to keep the system afloat.
Unions called for new nationwide strikes and protests on Tuesday, during King Charles III's planned visit to France.
That will coincide with the British king’s scheduled visit to Bordeaux on the second day of his trip to France.
Interior Minister Gerald Darmanin visited police headquarters on Thursday night as fires still burnt in some Paris neighbourhoods. He gave the assurance that security “poses no problem” and the British monarch will be “welcomed and welcomed well”.
There was “enormous degrading” of public buildings and commerce, “far more important than in precedent demonstrations”, he said.
“There are troublemakers, often extreme left, who want to take down the state and kill police and ultimately take over the institutions,” Mr Darmanin said.
With violence intensifying in recent days, he said that 12,000 members of the security forces were on the French streets on Thursday, with 5,000 in Paris.
The heavy wooden door of the elegant Bordeaux City Hall was set on fire and quickly destroyed by members of an unauthorised demonstration, according to the Sud Ouest.
More than a million people joined protest marches held in cities and towns around the country on Thursday, the Interior Ministry said.
Demonstrations were held a day after Mr Macron further angered his critics by refusing to back down on the retirement bill that his government forced through parliament without a vote.
“While the (President) tries to turn the page, this social and union movement … confirms the determination of the world of workers and youth to obtain the withdrawal of the reform,” the eight unions organising protests said.
They called for localised action this weekend and new nationwide strikes and protests on Tuesday.
Protests against pensions continue in Paris — in pictures
Strikes upended travel as protesters blockaded train stations, Charles de Gaulle Airport in Paris, refineries and ports.
In Paris, street battles between police and black-clad, masked groups who attacked at least two fast food restaurants, a supermarket and a bank reflected intensifying violence and drew attention away from the tens of thousands of peaceful marchers.
Police, pelted by Molotov cocktails, objects and fireworks, charged multiple times and used tear gas to disperse rioters. A haze of tear gas fumes covered part of the Place de l'Opera, where demonstrators converged at the march's end.
Mr Darmanin said radicals numbered some 1,500.
Violence marred other marches, notably in the western cities of Nantes, Rennes and Lorient — where an administrative building was attacked and the courtyard of the police station was set afire and its windows broken — and in Lyon, in the south-east.
Thursday's nationwide protests were the ninth union-organised demonstrations since January, when opponents still hoped that parliament would reject Mr Macron's measure to raise the retirement age.
But the government forced it through using a special constitutional measure.
In an interview on Wednesday, Mr Macron refused to budge from his position that a new law is necessary to keep retirement coffers funded.
Opponents proposed other solutions, including higher taxes on the wealthy or companies, which Macron says would hurt the economy. He insisted the government’s bill to raise the retirement age must be implemented by the end of the year.
The Constitutional Council must now approve the measure.
High-speed and regional trains, the Paris metro and public transportation systems in other major cities were disrupted. About 30 per cent of flights at Paris Orly Airport were cancelled.
The Eiffel Tower and the Versailles Palace, where the British monarch is set to dine with Mr Macron, were closed on Thursday due to the strikes.
Nadia Belhoum, a 48-year-old bus driver participating in the action, criticised Mr Macron’s decision to force the higher retirement age through.
“The president of the Republic … is not a king, and he should listen to his people,” she said.