At least 108 police were wounded and 291 people detained across France as violence erupted at May Day protests showing anger at President Emmanuel Macron's pension reform, according to an interior minister.
Such a high toll of police wounded was "extremely rare" for a 1 May protest day, Interior Minister Gerald Darmanin told reporters.
He added that one policeman who was hit by a Molotov cocktail had received burns to his face and hands, but his life was not in danger.
In the French capital, projectiles were thrown at police, ride-sharing bicycles were torched and bus stops vandalised just as the union-led march got under way from the central Place de la Republique.
Unrest also erupted in Lyon, where several vehicles were set ablaze and some business premises were trashed, television images showed. In Nantes in western France, a fire blazed in front of a local administration building.
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Mr Macron last month raised the retirement age by two years to 64 despite multi-sector strikes, in a move that drove his popularity down to near the record lows seen during the "Yellow Vest" crisis of 2018-2019.
The reform has crystallised discontent against a president perceived by many as aloof and indifferent to their daily hardships, and he has been met during walkabouts by heckling and pot banging.
"The executive cannot govern without the support of its people," Sophie Binet, leader of the hard-left CGT union, said ahead of the Paris protest, adding her union had not yet decided on talks with the government on other work-related matters.
Laurent Berger, head of the reform-minded CFDT trade union, said Mr Macron's government had been deaf to the demands of one of the most powerful social movements in decades.
He dismissed suggestions that a rare alliance between the leading trade unions was being tested now that the pension bill had been signed into law.
"We must bring other proposals over salaries and working conditions to the table," he told BFM TV.
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In Paris, Extinction Rebellion activists threw paint over the glass-fronted facade of the Louis Vuitton Foundation and paving stones outside the Ritz Hotel.
Elsewhere in Europe, union-led protests were planned across Germany. In Italy, the three main unions held a rally in the southern city of Potenza protesting against a labour package approved by Prime Minister Giorgia Meloni's rightist government.
In the northern city of Turin, anti-government protesters marched with a puppet of Meloni holding up her arm in a fascist salute.
During a parade in the Swiss city of Zurich, demonstrators threw water balloons at the emergency services, the windows of at least two banks were smashed and some properties were spray-painted, police said.
Mr Macron says the French reform is needed to help shore up one of the industrialised world's most generous pension systems.
French pension payments as a share of pre-retirement earnings are comfortably higher than elsewhere and a French man typically spends longer in retirement than those in other OECD nations.
Trade unions say the money can be found elsewhere.
Retired metalworker Michel Maingy said he felt the battle over pensions was lost. Even so, there were still fights to be won in negotiations over working conditions, he said.
"Little by little, we'll get back on track. We need to keep our chins up," he said ahead of the protest in Nantes.
Mr Macron's government, which lacks a working majority in parliament, rammed the pension legislation through without a final vote due to a lack of cross-party support.
A hardening of the political opposition risks complicating the rest of his reform agenda, including an employment bill that would require those receiving the minimum welfare benefit to work or get training for 15-20 hours per week.
Fitch cut France's sovereign credit rating on Friday by one notch to 'AA-', saying that the social unrest and potential political deadlock posed risks to Macron's agenda.
