Riot police have clashed with protesters as thousands of people joined protests in Paris ahead of the French presidential election.
Security officials were forced to protect themselves from flames as the marches turned ugly on Monday afternoon.
Tear gas was fired at groups of youths, while pictures from the scene showed broken glass and burning shopping trolleys.
It came as far-right leader Marine Le Pen and centrist Emmanuel Macron held high-stakes rallies overlapping with nationwide May Day union marches.
The tense campaigning interrupted the usual calm of the May Day holiday, as supporters of both candidates took to the streets, airwaves and social networks to weigh in on an election closely watched by global financial markets and France's neighbours as a test of the global populist wave.
Mr Macron, an independent, leads his far-right rival Marine Le Pen by around 20 percentage points in the polls.
Many used the traditional May Day union marches to stage a show of force against Le Pen, with some 250 events planned across France.
More than 9,000 security officers were reported to be mobilised on the streets of Paris, with instructions to stop and check vehicles and pedestrians.
The National Front traditionally holds a march in central Paris on May 1 to honour Joan of Arc. At the 1995 event, a group of skinheads broke away and pushed 29-year-old Brahim Bourram off a bridge into the Seine, where he drowned. Then-party leader Jean-Marie Le Pen sought to distance himself from the attackers, but the death drew national outrage.
Standing on the bridge, Mr Macron hugged Bourram's son Said, who was nine years old when his father was killed.
Said, now a chauffeur who supports Mr Macron, said his father was targeted "because he was a foreigner, an Arab. That is why I am fighting, to say no to racism".
Mr Macron insisted that despite Marine Le Pen's efforts to distance herself from her father's anti-Semitism, "the roots are there, and they are very much alive.
"I will not forget anything and I will fight to the last second, not only against her project, but against the idea she has of democracy and the nation."
Jean-Marie Le Pen was set to hold the Joan of Arc event again, a march his daughter wants nothing to do with. Instead, she is holding a rally in an exhibition centre north of Paris.
Marine Le Pen said on France-2 television that the political rupture with her father "is definitive".
She called it a "violent" decision for herself, but said she did it "because the higher interest of the country was at stake".
Her event was by Nicolas Dupont-Aignan, a conservative candidate from the first-round election who shocked many French by agreeing to be Ms Le Pen's prime minister if she wins the presidency.
Ms Le Pen, speaking on Europe-1 radio, reached out to "all those who are patriots" and who want to restore French borders and currency and "rediscover the voice of labour, defend our identity, fight against Islamic fundamentalism".