"They have a profound sense of social injustice," said Jean-Claude Mailly, head of the large Force Ouvriere union, "and that, I think, is something that neither the government nor the employers have understood."
Benoit Hamon, a spokesman for the French Socialist Party spokesman said France was experiencing similar problems to other countries, but that the situation was being made worse by President Nicolas Sarkozy.
"We have a president who aggravates the crisis by making the wrong economic and social choices, by his deafness regarding the general dissatisfaction," said Mr Hamom.
"He refuses to give answers regarding layoffs, regarding the cost of living, regarding the way to objectively avoid the rise in job losses in the public sector or in the public health system."
Marches were also being held in Marseille, Lyon, Grenoble and many other towns and cities.
Noel Kouici, demonstrating in Marseilles, said protesters had a "grudge" against the government.
"Of course we are angry against the government when you see the way they serve the banks and leave the people starving and losing their jobs," he said.
But the deputy mayor of Marseille, Roland Blum, told the BBC the government had done a lot to help people.
"Of course I understand the distress of people who've lost or are going to lose their jobs, but what I think is necessary is that we all work together," he said.
There protests were largely peaceful but minor scuffles were reported in several cities later in the evening.
In Paris, police used tear gas to disperse small groups of youths who were setting fire to rubbish bins and throwing bottles.
It is the second time in two months that major demonstrations have been held, following a similar display in January which drew about a million protesters.
The strikes began on Wednesday evening on transport networks.
French commuters face a limited rail service because of the strike
The national rail operator, SNCF, cancelled 40% of high-speed trains and half of regional services.
A third of flights out of Paris's Orly airport have been cancelled, while a tenth of France's electricity output has been shut down with workers on strike.
However, buses and the Metro rail system in Paris were running normally, thanks to a new law enforcing a minimum transport service during strikes,.
But with many schools and public buildings shut for the day, the number of workers travelling into the capital was reduced.
Private-sector firms were also expecting a depleted workforce, with staff from the beleaguered car industry, oil and retail sectors taking part in the strike.
The unions say the 26bn euro ($35bn; £24.5bn) stimulus package for France's struggling economy, unveiled by Mr Sarkozy in December, does not go far enough.
FRENCH UNIONS vs GOVERNMENT
Increase minimum wage
Reverse 50% cap on income tax
Suspend public sector job cuts
Measures to protect employment
Government stimulus plan
11bn euros to help businesses improve cashflows
11bn euros of direct state investment
4bn euros of investment by state-owned firms in modernisation
2.65bn euros of tax breaks, and increases in family welfare and short-term unemployment benefits
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