Train drivers were among those to walk out in protest at planned pension reforms.
The changes would see the retirement age rise by two years to 64.
The walkouts left public transport severely disrupted, with few high-speed trains running and some Paris metro stations closed.
Though at least some travellers backed the strikers.
It's a necessary expression of opposition to the reforms says this man.
Strikes and protests extended across the country.
Some seven out of ten primary school teachers are expected to walk out.
Power firm EDF said electricity output was down by about 12%.
Shipments were blocked at some oil refineries.
And about 20% of flights were cancelled at Paris's number-two airport, Orly.
It all raises the pressure on the government of President Emmanuel Macron.
Ministers say the reforms are "necessary and fair", and will allow the pension system to break even.
Unions say there are other ways to raise the needed money, such as taxes on the super-rich.
Now the strikes will test which side of the argument has public support.
