By Caroline Wyatt
BBC News, Paris
From Place de la Republique all the way to Bastille, the streets of Paris were a colourful mass of strikers bearing banners and balloons, amid a good-natured, almost carnival atmosphere.
Up to 30% of public workers are said to have joined the strike
The smell of frying hamburgers, kebabs and merguez sausages wafted through the crowds, as public sector workers gathered for a show of trade union muscle.
Hundreds of thousands of protesters were taking part in similar rallies across France, called by five of France's main unions in protest at French government policy.
Teacher Bruno Mer was typical of many marching in Paris today.
He teaches at a school in a deprived suburb of the capital, where most of his pupils come from immigrant families and few speak French as their first language.
He told me he marched not just for himself or higher wages for teachers in general, but for more government spending for the poorest in French society.
He firmly believes that premier Dominique de Villepin's government is helping the rich in France at the expense of the poor.
"Things are getting pretty bad in France," he said. "We have big social problems, and the choices made by this government favour the upper and the middle classes, not the poor."
Yet in much of Paris, life went on as usual.
Restaurants and cafes stayed open: the private sector was very much at work today.
At Sept Bis, a crowded restaurant in the business district of Paris, owner Benedicte Chauvet said she was getting fed up with public sector workers demanding more job security, and an ever bigger slice of a dwindling public pie.
"I don't feel any solidarity with the strikers," she said, watching as the waiters rushed between tables, miraculously balancing trays piled high with a traditional French lunch.
"This is supposed to be a strike by public and private sector workers, but most of the strikers are in the public sector.
"They are privileged enough already: they have job security, decent salaries and a guaranteed pension. I'm part of a very different France - a more dynamic France. So I don't feel a lot of sympathy for them."
But on Place de la Republique, the demonstrators insisted they were protesting on behalf of all French workers, whether in the private or public sector, for equality and social justice.
From school teachers to train drivers, all believe their wages are too low and that their fabled job security is fading fast as the government implements its economic reforms.
French unions say the action is a necessary protest
Postal worker, Herve Grohan, is unconvinced by Mr de Villepin's arguments that the French state must tighten its belt and that the country is living beyond its means.
He disagrees strongly with the government's move to make it easier to hire and fire workers at smaller companies, even though the changes will not affect him directly.
Mr Grohan, 32, also believes higher wages in the public sector would stimulate spending and help create new jobs.
"I know the government doesn't have a lot of money, but if they paid people more, the money would be used and would go back into the economy."
The French trade unions warn that if the government does not listen to their litany of grievances, this could be the start of a long autumn of discontent in France, and an uncomfortable time for the French prime minister.
Mr de Villepin was appointed at the end of May to deal with a France whose divisions had just been laid bare by its rejection of the European Constitution in a referendum that month.
This national "day of action" was the first real test of his mettle since coming to office.
French business leaders are waiting to see whether he will give in to the pressure from the streets, or whether he will continue with difficult, unpopular, but perhaps necessary reforms aimed at helping the country compete in a globalised economy.