France's interior minister promised Wednesday to boost security at protests after hooded youths ran amok at May Day demonstrations in Paris, torching cars and a McDonald's restaurant.
Police said 109 people were in custody after the violence, which has sparked criticism in the press that the government was unprepared for 1,200 black-clad troublemakers joining the traditional May 1 protests for workers' rights.
"The authority of the state, reduced to statements of 'strong condemnation', has been tarnished once again," read a column in the right-leaning Figaro newspaper.
Regional daily L'Est Republicain deplored "the sight of these 1,200 thugs dressed in black on the Austerlitz bridge", while the L'Alsace newspaper declared: "Governing means planning ahead."
Interior Minister Gerard Collomb pledged to look again at how to police protests given the rise of far-left "black bloc" protesters who turn up with the intention of attacking police or property.
"For the next demonstrations there will be even more security forces, this time with the intention of totally separating protesters from those who have come to smash things up," Collomb told France 2 television.
But he defended the way police had handled the violence, saying little could be done to stop trouble-makers from infiltrating the crowds.
"We can only detain a certain number of people who turn up like you or I in civilian clothing and then suddenly are dressed in black bloc outfits in the middle of the crowd," he said.
"We cannot keep up, even with 21 police units mobilised against movements which all of a sudden appear on a scale we've never seen before."
President Emmanuel Macron, on a visit to Sydney, deplored the clashes in the French capital, one of several cities around the world where May Day protests turned violent.
"May 1 is Workers' Day, not the day of the hooligans," he told a press conference.
Shouting "Rise up, Paris" and "Everyone hates the police", anti-capitalist protesters in black jackets and face masks had tried to hold up the Paris march.
They lobbed projectiles at security forces along the route, who responded with volleys of tear gas and water cannon.
Youths ransacked and then set fire to a McDonald's restaurant near Austerlitz station, east of the city centre, and torched vehicles at a car dealership, leaving smoke billowing into the air.
"We are sick of this capitalist system that destroys everything, of brutal police repression of those who oppose them," one masked protester, identifying themselves as a 19-year-old student, told AFP.
Police said 31 shops and businesses had been damaged, while six cars were burned and another 10 smashed up. On Tuesday, nearly 300 people had been detained.
Four people were injured, including a riot officer hurt when a stone was thrown at his back.
"The black blocs are discrediting everything," complained 54-year-old protester Mathieu Gourmelon, who came with his family.
The violence marred the larger peaceful protest by union activists and others -- 20,000 according to the police, 55,000 according to the CGT union -- demonstrating against Macron's public sector reforms.
The business-friendly centrist has implemented controversial labour reforms designed to make it easier to hire and fire in France, and pledged to cut 120,000 public sector jobs.
Some students object to his bid to make university access more competitive, while rail workers have unleashed three months of rolling strikes over his planned shake-up of state operator SNCF.