France's largest nationwide strike in years has severely disrupted schools and transport, reports BBC News.
Workers are angry about planned pension reforms that would see them retiring later or facing reduced payouts.
Teachers and transport workers have been joined by police, lawyers, hospital and airport staff, and other professions for a general walkout.
President Emmanuel Macron wants to introduce a universal points-based pension system.
That would replace France's current system, which has 42 different pension schemes across its private and public sectors, with variations in retirement age and benefits.
"What we've got to do is shut the economy down," said Christian Grolier official with the union Force Ouvrière (Workers' Force). "People are spoiling for a fight."
Since coming to power, Mr Macron has pushed through other reforms including relaxing labour laws and cutting taxes for businesses.
By 16:00 local time (15:00 GMT), 450,000 people had joined demonstrations in 40 cities across France, not including Paris. The CGT union said 250,000 had marched in Paris.
The CGT also said workers had blocked seven of the country's eight oil refineries, potentially causing fuel shortages if the strike continues.
In Paris, popular tourist sites including the Eiffel Tower, the Musée d'Orsay and the Palace of Versailles shut for the day.
There were also reports of clashes between protesters and police. By 17:00 local time, police in Paris had detained 87 people, officials said. In the western city of Nantes, protesters were tear-gassed after some threw projectiles at police.
- Some 90% of high-speed TGV and inter-city trains have been cancelled
- In Paris, just five of the city's 16 metro lines are running
- Train operators Eurostar and Thalys have cancelled at least half their services linking Paris with London and Brussels. Eurostar will operate a reduced timetable until 10 December
- Hundreds of flights have been cancelled
- Air France has cancelled 30% of internal flights and 10% of short-haul international flights amid walkouts by air traffic controllers
- Low-cost carrier EasyJet has cancelled 223 domestic and short-haul international flights, and warned passengers to expect delays.
Meanwhile the Extinction Rebellion group said it had sabotaged thousands of e-scooters by painting over the QR codes that smartphone users scan to unlock the vehicles.
The group said this was because e-scooters - despite being widely viewed as an ecologically-friendly form of transport - actually required large quantities of energy and resources during their manufacture and had short life cycles.
Train driver Cyril Romero from Toulouse told France Info he would reconsider his job if the reforms went through.
"I started in 2001 with a contract that allowed me to leave at 50. But like everyone else, I got the reforms which pushed back my early retirement age to 52-and-a-half and then, in reality, 57-and-a-half for full pension. Now they want to make us work even longer."
An unnamed history teacher, writing in HuffPost, was planning to strike on Friday as well as Thursday.
"For me, the pension reforms are one punch too many. We're fighting not to lose hundreds of euros of pension a month - after more than 40 years in a job.
"How can you even dream of ending your career in front of pupils beyond the age of 70, in worsening conditions and on what for many of us is just a minimum wage?"