Industrial action over labour law reforms is gripping France nationwide, with oil refineries, nuclear power stations and transport hubs affected.
Motorways and bridges were blocked and flights delayed, and 16 arrests were made as a result of clashes in Paris.
Prime Minister Manuel Valls insists the reforms will not be withdrawn but has suggested they could be "modified".
The action, building over three months, comes two weeks before France hosts the Euro 2016 football championships.
A state of emergency imposed after November's deadly attack by militants from the co-called Islamic State group in Paris remains in place.
The CGT union is leading the action, supported by six other unions including Force Ouvriere and Unef, whereas the more moderate CFDT union backs the labour reforms.
Dozens of people broke away from the demonstration in Paris and set about smashing shop windows and parked cars in a side street.
Masked youths hurled bottles at police, who responded with tear gas.
Elsewhere in France on Thursday:
- Clashes broke out in the eastern city Lyon after a march by at least 3,300 protesters
- In the port city of Le Havre, in Normandy, hundreds of workers took to the streets after blocking off a major bridge
- Riot police held back protesters in the central city of Tours
- Demonstrators invaded high-speed railway lines in the western city of Rennes
- Protest marches were reported in the southern cities of Marseille, Montpellier and Bordeaux
Flights to and from Paris, Nantes and Toulouse have been affected, and a rolling strike by train drivers has brought further disruption to regional and commuter rail services.
CGT union members at nuclear power plants voted on Wednesday to join the strike, and the union said 16 of the country's 19 power stations would be affected.
Nuclear power provides about 75 percent of the country's electricity. Grid operator RTE said nuclear power capacity was being cut by at least four gigawatts, equivalent to 6 percent of the country's total production capacity, on Thursday, Reuters news agency reports.
Six of France's eight oil refineries have already been hit by strikes and barricades, as have major ports including Marseille and Le Havre.
As the union action ramped up on Thursday morning, Mr Valls indicated there might "still be changes, improvements" made to the labour reform laws.
But he rejected Finance Minister Michel Sapin's suggestion that Article 2 of the bill could be rewritten. Article 2 gives individual companies the power to opt out of national obligations on labour protection if they feel they need to - something the CGT union is fiercely opposed to.
Pumps running dry
The French Union of Petroleum Industries says a third of France's 12,000 petrol stations are now running dry.
It said the government had begun using its strategic fuel reserves, which analysts say will last around four months.
Transport Minister Alain Vidalies said 40% of petrol stations around Paris were struggling to get fuel.
Unions were enraged by the government's decision to use a constitutional device allow its watered-down labour reforms to be made into law without parliamentary approval.
The government says the reforms, which make it easier for companies to hire and fire staff, are needed to bring down unemployment.