Nicolas Sarkozy, the long-time frontrunner in France's presidential contest, enlisted the support of his wife, Cecilia, today as millions of French cast their votes in the first round of a very tight contest to find a replacement for Jacques Chirac.

The most visible of all voters were the 12 presidential candidates, including the Socialist Ségolène Royal, who cast her ballot in the small town of Melle in her political heartland in western France.

“The French people know the importance of this vote," she told reporters. "I share their feeling that this is a very important day."

With no candidate expected to achieve an overall majority in today's first round, it will come down to a second round of voting on May 6 between the two frontrunners.

Hopes that Francois Bayrou, the centrist "wild card", could snare a place in the run-offs were hit by late opinion polls showing his support crumbling and Ms Royal gaining ground on Mr Sarkozy, the hardline former interior minister.

A CSA poll, which was not published in France because of a black-out before today's ballot, put Ms Royal on 26 per cent, only a point behind Mr Sarkozy.

Jean-Marie Le Pen, the leader of the far-right National Front who set off shockwaves around the world when he grabbed a place in the run-offs at the last presidential election in 2002, was said to be lying third on 17 per cent, a point ahead of Mr Bayrou.

Perhaps the most significant figure thrown up by the poll was the fact that almost four in ten voters were still undecided after a campaign in which none of the major candidates are thought to have distinguished themselves and in which policy has played second fiddle to personality.

Mr Sarkozy, an abrasive character who is accused by his critics of being overly authoritarian, underwent a public split from his wife in 2005 when she left him for a New York advertising executive, complaining that he treated her like "a piece of furniture".

The two reconciled early last year, but Cecilia, the daughter of a Russian pianist, has been all but invisible in recent weeks, prompting speculation - fuelled last week by Mr Le Pen - that their relationship is in trouble.

Today's joint appearance seemed designed to quash that speculation and Mr Sarkozy was all smiles as he and his family arrived on foot at the Neuilly polling station.

“What is very important is that the French come to vote in large numbers,” he told reporters in Neuilly, a suburb of Paris.

By midday 31 per cent of the country's 44.5 million registered voters had turned out, far more than in 2002 - and some said that Mr Le Pen's first-round success last time had shaken them out of their apathy.

“I want it to be a Sarkozy-Segolene run off,” Laurence Rouquette, a 40-year-old antiques dealer, said after voting in a sunny Paris suburb. “Usually I vote for the smaller candidates but this time I voted for one of the main ones.”

Mr Sarkozy, the son of a Hungarian immigrant, has pushed a right-wing programme based on the themes of work and national identity and is seen as the most business-friendly of the candidates. But his tough talk sparked fears he would divide rather than unite the nation.

Ms Royal, an army officer’s daughter with an almost permanent smile, has presented herself as a nurturing mother figure and has proposed a leftist economic programme that would keep France’s generous welfare system intact. Meanwhile, Mr Bayrou, a former Latin teacher, wants to end the left-right political divide by forming a national unity government.

All three mainstream candidates come from a new generation of politicians - all are in their fifties - and all claim to represent a break from a discredited past.

Whoever ends up winning the presidency in two weeks' time will also have to deal with a huge public debt, stubbornly high unemployment and seething discontent in immigrant suburbs which erupted into widespread rioting two years ago. He or she will also need to soothe French angst about factories closing and jobs relocating to China or India.

Also running in the election are three Trotskyites, a Communist, a Green and Jose Bove, a well-known anti-globalisation campaigner. They are joined by a Catholic nationalist and a campaigner for hunters' rights.

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