Forty people were hurt and dozens arrested on Tuesday as violence between riot police and masked troublemakers gripped huge Paris protests over France's labour reforms.
Police fired water cannons in the south of the French capital to quell rioters as "several hundred" masked protesters lobbed objects at security forces.
As tens of thousands of people took to the streets in nationwide protests against the controversial labour reforms, strikes closed the Eiffel Tower and disrupted transport links.
Police said 29 members of the security forces were among those wounded in Paris, while three cars were burned on the city streets.
The international spotlight is on France as the host of the Euro 2016 football championships, which has also been marred by violence between fans.
Tens of thousands of fans are continuing to pour into the country for Europe's showcase football event.
In Paris, several demonstrators stormed a building site and hurled wooden pallets at riot police.
Protesters shouting "Paris, rise up" and "everyone hates the police" smashed shop windows and targeted banks in running battles with officers.
One man was led away by officers in riot gear with blood dripping from a wound above his eye onto his white T-shirt.
The strikes were the latest in months of industrial action that have caused severe disruptions to air and rail transport, hit fuel supplies and led to mountains of rubbish on the streets of Paris.
"I've been to all the demos since March because I want to live in dignity, not just survive," said Aurelien Boukelmoune, a 26-year-old technician marching in Paris.
"I want the reforms to be withdrawn, pure and simple. Only then will it stop. For the government's sake, they should withdraw the law, otherwise we'll block the economy."
Police and organisers gave wildly different figures for the turnout, with unions saying 1.3 million people had turned out across France but police estimating the crowds at 125,000 or more, some 80,000 of them in Paris.
With France on high alert over fears of attacks during Euro 2016, overstretched security forces had feared the demonstrations could turn violent and banned 130 known troublemakers from taking part.
The terrorism threat was thrust back into the spotlight after a man claiming allegiance to the Islamic State group stabbed to death a deputy police chief and his wife, who also worked for the police, at their home in a northwestern Paris suburb late on Monday.
The latest in a wave of protests that began in March coincides with a French Senate debate on the reforms, which are aimed at making the job market more flexible and reducing high unemployment but which critics see as too pro-business.
President Francois Hollande's Socialist government voiced hope the latest day of protest would be a last stand for the movement.
Philippe Martinez, head of the far-left CGT union that spearheaded last month's blockades of fuel depots and an ongoing rail strike, had promised a "very strong mobilisation".
In Marseille, organisers said 140,000 turned out, compared with a police estimate of 5,000.
Two further protest days are set for later this month.
At a time when the French capital would normally be reaping the benefits of high-season tourism boosted by the football, the demonstrations have dampened the flow to the world's most-visited city.
Several staff at the Eiffel Tower went on strike, leaving insufficient numbers to open the monument safely, according to its operator, SETE.
Adding to the climate of discontent, rail workers continued strike action to protest working conditions. They were joined at the weekend by a minority of Air France pilots.
The pilots' strike, which affected about one in five flights according to the airline, was set to end on Tuesday, while the rolling strike at national rail company SNCF was in its 14th day.
The actions have further depressed France's tourism sector, already hit by the November attacks in Paris that left 130 people dead.
Hollande, who faces a re-election bid next April, had hoped the signature reform would reverse his approval ratings, which are among the worst of a modern French leader.
His government sparked fury when it pushed the reforms through parliament without a vote, with a little-used political device.
While rejecting union demands to withdraw the bill, the government has watered it down, notably by scrapping a cap on severance pay.