Paris: French voters choose on Sunday whether a pro-European Union centrist or a eurosceptic, anti-immigration far-rightist will lead them for the next five years, with early figures indicating turnout could be low, but above most recent forecasts.
Opinion polls predict that after 8 p.m. (1800 GMT) Emmanuel Macron, a 39-year-old ex-economy minister who wants to bridge the left-right divide, will be named as president, seeing off the challenge from National Front leader Marine Le Pen.
A Macron victory would further stem the tide of nativist, anti-globalisation voting outcomes like those that will see Britain quit the EU and which made Donald Trump U.S. president.
Macron, who wants to deregulate the economy and deepen EU integration, is set to win the head-to-head with between 61.5 and 63 per cent of the vote, according to the last opinion polls on Friday.
Should an upset occur and Le Pen win, the very future of the EU could be on the line given her desire to close borders, dump the euro currency, and tear up trade treaties.
Even in defeat, her vote is likely to be about twice what her party scored the last time it reached the presidential second round in 2002, demonstrating the scale of voter disaffection with mainstream politics in France.
Midday turnout figures from the Interior Ministry said 28.23 per cent of voters had turned out so far, the lowest at this stage of the day since the 2002 presidential poll, when it was 26.19 per cent.
Turnouts at midday in 2012 and 2007 were 30.66 per cent and 34.11 per cent respectively.
A poll on Friday had predicted a final turnout of 75 per cent this time.
The eventual turnouts in 2002, 2007 and 2012 were all above 80 per cent.
Pollsters see abstentions as likely to be highest among left-wing voters who feel disenfranchised by the second-round choice, but it is unclear what a high or low turnout could mean for the outcome.
Nevertheless, voter surveys forecasting the result itself proved accurate for the first round last month which eliminated nine other candidates in a tight race.
Markets have risen in response to Macron's widening lead over his rival after a bitter television debate on Wednesday.
"We increased our equity exposure and added some French stocks after the first round," said Francois Savary, chief investment officer at Geneva-based fund management firm Prime Partners.
"The major political risk of a Le Pen victory appears to be disappearing."
After a campaign in which favourites dropped out of the race one after the other, Le Pen is nevertheless closer to elected power than the far right has been in France since World War II.
If opinion polls prove accurate and the country elects its youngest-ever president rather than its first female leader, Macron himself has said himself he expects no honeymoon period.
Close to 60 per cent of those who plan to vote for Macron say they will do so to stop Le Pen from being elected to lead the euro zone's second-largest economy, rather than because they fully support the former banker turned politician.
"I don't necessarily agree with either of the candidates," psychotherapist Denise Dulliand, who was voting in Annecy in the mountainous southeast, told Reuters.
"But I wanted to express my voice, to be able to say that I came, even if I am really not satisfied with what is happening in our country, and that I would like to see less stupidity, less money and more fraternity."
The battle between mainstream and more radical policies in France will continue into parliamentary elections next month in which the new president will try to secure a majority in parliament.
One poll this week suggested that was within reach for Macron.
Much will also depend on how the candidates score on Sunday.
Le Pen's niece, Marion Marechal-Le Pen, on Thursday told L'Opinion daily that winning 40 per cent of the vote would be "a huge victory" for the National Front.
Whoever wins will open a new chapter in French politics, after the major left- and right-wing parties -- the Socialists and The Republicans -- that have ruled France for decades both suffered humiliating defeats in the election's first round.
The campaign was hit by yet another surprise on Friday night, just as the quiet period in which politicians are forbidden from commenting began.
Macron's team said a massive hack had dumped emails, documents and campaign-financing information online.
Exit polls will be published when voting ends at 8 pm (1800 GMT).
With security a prime concern More than 50,000 police officers were on duty on Sunday.
A series of militant attacks in Paris, Nice and elsewhere in France have killed more than 230 people in recent years.