- Strike action by unions at French oil refineries, nuclear power stations, ports and transport networks is leading to serious nationwide disruption, BBC News reports.
PM Manuel Valls has again insisted that labour reforms at the heart of the dispute would not be withdrawn, but suggested they could be "modified".
Striking workers have blockaded motorways and bridges, as well as a nuclear submarine base in Normandy.
Nuclear power production has slowed, and fuel remains in short supply.
Flights to and from Paris, Nantes and Toulouse have been affected, and a rolling strike by train drivers is expected to further disrupt regional and commuter rail services.
The unions have called for rallies in most major cities.
Hundreds of workers blocked access to the Bridge of Normandy outside the key port city of Le Havre. The Associated Press reported strikers were throwing smoke bombs into fountains in the city itself.
CGT union members at nuclear power plants voted on Wednesday, May 25 to join the strike, and the union said 16 of the country's 19 power stations would be affected.
Nuclear power provides about 75% of the country's electricity. Grid operator RTE said nuclear power capacity was being cut by at least four gigawatts, equivalent to 6% 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, Valls indicated "there may 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.
