More than 44 million French voters were called to the polls on Sunday for the first round of a presidential election that may see the end of Nicolas Sarkozy's turbulent term in office.

Predictions of a high abstention rate and strong protest vote left the outcome uncertain, but all opinion polls point to the right-wing incumbent coming second to his Socialist challenger Francois Hollande.

The two 57-year-old political veterans are thus on course to face each other head-to-head in a May 6 run-off, which will decide who runs what is commonly regarded as the world's fifth greatest power for the next five years.

French citizens living overseas began voting early, with those in Brazil, Uruguay and Argentina and in France's overseas territories -- islands dotting the Atlantic, Pacific and Indian oceans -- starting Saturday, while citizens in Australia and New Zealand began voting early Sunday.

In France polling was to open at 8.00am (0600 GMT) and continue to 8.00pm, whereupon voting estimates based on ballot samples will immediately be published, giving a traditionally accurate picture of how the candidates did.

In all, ten are in the race, Hollande and Sarkozy being trailed by far-right flag-bearer Marine Le Pen, hard-left firebrand Jean-Luc Melenchon and veteran centrist Francois Bayrou and a handful of outsiders.

The campaign has run on for months but has yet to inspire much passion, except for a series of mass open-air rallies by supporters of Melenchon, whose Communist-backed Left Front coalition has made a strong breakthrough.

Once the first round is out of the way, Sarkozy and Hollande will face each other in a two week scramble for the line, including a head-to-head televised debate that could be the incumbent's last chance to change his fortunes.

An average of eight opinion polls conducted on Friday showed Hollande comfortably beating Sarkozy next month by approximately 55 percent to 45.

The final fortnight is expected to see some bitter exchanges.

Hollande says Sarkozy has trapped France in a downward spiral of austerity and job losses, while Sarkozy say his rival is inexperienced and weak-willed and would spark panic on financial markets with reckless spending pledges.

But there was little sign of such rhetoric on Saturday, as French law prohibits campaigning and opinion polls on the eve of voting.

Voters went about their business without being accosted by pamphleteers, the campaigns' websites, Facebook pages and Twitter feeds were left without updates and broadcasters had to find other subjects to interview.

Some hints of the campaigns' moods slipped past the censors.

"Lovely day," wrote Socialist Party spokesman Benoit Hamon on his personal Twitter account, linking to an upbeat song by Ella Fitzgerald, and tacitly suggesting that the left remains coolly confident.

The left-wing daily Liberation emblazoned its front page with the headline "A strong left" against the backdrop of a blue ocean under open skies, mocking the slogan and imagery of Sarkozy's "A strong France" campaign.

The pro-Sarkozy Le Figaro stuck doggedly behind its champion, but doubts clouded its front page editorial, which warned all those thinking of voting far-right or centrist that the second round would depend on the first.

Privately, Sarkozy's top supporters have begun to admit that if Sarkozy fails to regain the momentum and slip ahead of Hollande on Sunday, he will have too much ground left to make up before the May 6 showdown.