Protesters clashed with security forces across France on Monday as hundreds of thousands of people took to the streets for labour day to vent their anger against President Emmanuel Macron's pension reform.

Unions had been hoping for a vast turnout across France for the May 1 protests to further rattle Macron, who has been greeted by pot-bashing and jeers as he toured the country seeking to defend the reforms and relaunch his second mandate.

Macron last month signed a law to raise the retirement age from 62 to 64, despite months of strikes against the bill.

In Paris, radical protesters threw projectiles at police and broke windows of businesses such as banks and estate agents, with security forces responding with tear gas and water cannon, AFP correspondents said.

One policeman, hit by a Molotov cocktail, has suffered severe burns to the hand and to the face, Paris police told AFP. The police said 46 people have been arrested in the capital alone so far.

Police had been given a last-minute go-ahead to use drones as a security measure after a Paris court rejected a petition from rights groups for them not to be used.

Police used tear gas in Toulouse in southern France as tensions erupted during the demonstrations,while four cars were set on fire in the southeastern city of Lyon.

In the western city of Nantes, police also fired tear gas after protesters hurled projectiles, AFP correspondents said. The windows of Uniqlo clothing store were smashed.

"Even if the vast majority of demonstrators were peaceful, in Paris, Lyon and Nantes in particular the police face extremely violent thugs who came with one objective: to kill cops and attack the property of others," said Interior Minister Gerald Darmanin on Twitter.

The CGT union said 550,000 people had turned out in Paris for the protests and 2.3 million across France. Government estimates, likely to be far lower, are due later.

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Relaunch difficulties

Macron and his government have tried to turn the page on the months of popular discontent, hoping to relaunch his second term after the reform was signed into law.

"The page is not going to be turned as long as there is no withdrawal of this pension reform. The determination to win is intact," said CGT chief Sophie Binet at the Paris protest.

"The mobilization is still very, very strong," added Laurent Berger, head of the CFDT union.

"It is a sign that resentment and anger are not diminishing."

Monday marked the first time since 2009 that all eight of France's main unions have joined in calling for protests.

Radical ecological activists from Extinction Rebellion earlier sprayed orange paint on the facade of the glitzy Fondation Louis Vuitton museum in Paris, which is backed by the LVMH luxury goods giant.

In a separate action by a different environmental protest group, activists sprayed orange paint around the Place Vendome in central Paris, known for its jewellery shops, targeting the facade of the ministry of justice.

Macron's 'red card'

France has been rocked by a dozen days of nationwide strikes and protests against Macron and his pension changes since mid-January, some of which have turned violent.

But momentum has waned at recent strikes and demonstrations held during the working week, as people appear unwilling to continue to sacrifice pay.

When Macron attended the final of the French football cup on Saturday, he was met with activists waving red cards.

Almost three in four French people were unhappy with Macron, a survey by the IFOP polling group found last month.

Prime Minister Elisabeth Borne, with Macron's support, invoked in March the controversial article 49.3 of the constitution to ram the pension reform through parliament without a vote in the hung lower house.

In the Place de la Republique where the march started in the French capital, a huge vest with the slogan 'Macron resign' was fixed to the giant statue symbolising the French republic at its center. 

May Day demonstrations on a smaller and less fractious scale took place across Europe, including Spain where flag-waving demonstrators joined more than 70 rallies under the slogan: "Raise wages, lower prices and share profits."

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