The first round of polls is projected to produce a run-off rematch between incumbent Emmanuel Macron and far-right leader Marine Le Pen that could be far tighter than their duel five years ago.
France is voting in the first round of a presidential election, with far-right candidate Marine Le Pen posing an unexpected threat to President Emmanuel Macron's re-election hopes.
Voting began at 0600 GMT on Sunday and will end at 1800 GMT, at which time the first exit polls, will be published. Such polls are usually very reliable in France.
Voter turnout was 25.5 percent by midday (1000 GMT), the interior ministry said, below the 28.5 percent corresponding rate in the 2017 poll.
Until just weeks ago, opinion polls pointed to an easy win for Macron, the political centrist who was boosted by his active diplomacy over Ukraine, a strong economic recovery and the weakness of a fragmented opposition.
But his late entry into the campaign — with only one major rally that even the pro-European Union leader's supporters found underwhelming — his focus on an unpopular plan to increase the retirement age and a steep rise in inflation have dented his ratings.
In contrast, the anti-immigration, eurosceptic far-right Le Pen has toured France confidently, all smiles, her supporters chanting "We will win! We will win!".
She has been boosted by a months-long focus on cost of living issues and a big drop in support for her rival on the far-right, Eric Zemmour.
For sure, opinion polls still see Macron, 44, leading the first round and winning a runoff against Le Pen, 53, but several surveys now say this is within the margin of error. Twelve candidates are in the race in the first round, with the top two set to face the run-off on April 24.
"We are ready, and the French are with us," Le Pen told cheering supporters in a rally on Thursday, urging them to cast a ballot for her to deliver "the fair punishment which those who have governed us so badly deserve".
Macron, who became France's youngest president in 2017, spent the last days of campaigning trying to make the point that Le Pen's programme has not changed despite efforts to soften her image and that of her National Rally party.
"Her fundamentals have not changed: it's a racist programme that aims to divide society and is very brutal," he told Le Parisien newspaper.
Le Pen, who is making her third attempt to become France's first woman president, rejects allegations of racism and says her policies would benefit all French people, independently of their origins.
Assuming that Macron and Le Pen go through to the runoff, the president faces a problem: many left-wing voters have told pollsters that, unlike in 2017, they would not cast a ballot for Macron in the runoff purely to keep Le Pen out of power.
Macron will need to persuade them to change their minds and vote for him in the second round.
Sunday's vote will show who the unusually high number of late undecided voters will pick, and whether Le Pen can exceed opinion poll predictions and come out top in the first round.
French overseas territories voted on Saturday, starting with the island of Saint Pierre and Miquelon off the coast of Canada and then territories in the Caribbean followed by French Pacific islands.