The rallies, which polls say are backed by three-quarters of the French public, reflect growing disillusion with Sarkozy's reforms as tens of thousands jobs are lost to the downturn.

Several hundred youths clashed briefly with police at the end of the main union rally in Paris, highlighting the tensions in France, which has a long tradition of public demonstrations.

Spring sunshine helped Thursday's turnout, which unions said easily exceeded the numbers seen on a first day of nationwide protests staged on January 29.

But despite the crowds, French Prime Minister Francois Fillon flatly rejected demands for more state aid, saying there were no plans for further stimulus measures.

Streets in central Paris were packed with protesters waving anti-Sarkozy placards and chanting slogans, with badges reading "Get lost you little jerk!," a comment made by Sarkozy to a protestor at an agriculture show, much in evidence.

More than two million people are out of work in France and even many with a job struggle with the high cost of living.

A large public sector payroll and a relatively generous welfare state has kept French people better protected than many in other countries, but there has been deep public anger at a recent wave of plant closures and stories of corporate excess.

LASHING OUT AT BOSSES

Sarkozy, elected in 2007 on a pledge to shake up the French economy, has seen his approval ratings plunge as he has poured billions into bailing out banks and carmakers, but rejected union demands for higher pay and tax hikes for the rich.

"People are in the streets and they are suffering, there are more and more people out of work and something has to be done," said Sylvie Daenenck, marching in Paris. "We shouldn't just be giving money to the bosses."

Fillon told French television that executives should stop receiving "astronomical salaries," but ruled out throwing more money to kick-start the economy, saying France could not risk adding to its budget deficit, which is set to double this year.

"There is certainly not going to be a new stimulus plan," he said, adding that earlier measures had not yet kicked in.

The government introduced a 26 billion euro ($36 billion) stimulus plan last year aimed at business investment, and Sarkozy offered 2.65 billion euros of additional aid following the January 29 strike to help households weather the storm.

Union leaders are convinced the government will eventually have to concede more ground and meet their long list of demands, which includes a hike in low salaries and more job protection.

A series of disputes, ranging from strikes by university staff to violent protests by workers at a tire plant in northern France, have underlined a worsening climate of discontent that the government fears could escalate.

The CGT said 3 million people joined Thursday's protests in Paris and provincial towns and cities. The interior ministry said only 1.2 million took part.

Transport, energy and some government offices were all hit by the strike, although most trains, flights and metro networks were running near normal for much of the day.

French bosses have criticized the protests, saying the flailing economy cannot afford such regular stoppages.