France votes on Sunday 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.

Until just weeks ago, opinion polls pointed to an easy win for the pro-European Union, centrist Macron, 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 his supporters found underwhelming, and his focus on an unpopular plan to increase the retirement age, have dented the president's ratings, along with a steep rise in inflation.

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 leading the first round and winning a runoff against Le Pen on April 24, but several surveys now say this is within the margin of error.

Voting starts at 8 a.m. (0600 GMT) and ends at 1800 GMT, at which time the first exit polls, will be published. Such polls are usually very reliable in France.

"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, 44 and in office since 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 rejects allegations of racism and says her policies would benefit all French people, independently of their origins.

RUNOFF RISKS FOR MACRON

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, 53, can exceed opinion poll predictions and come out top in the first round.

"Marine Le Pen has never been this close to winning a presidential election," Jean-Daniel Levy, of Harris Interactive pollsters, said of Le Pen's third run at the Elysee Palace.

Supporters of hard-left candidate Jean-Luc Melenchon, running third according to opinion polls, hope for another kind of surprise, and have called on left-wing voters of all stripes to switch to their candidate and send him into the runoff.

Macron and Le Pen agree the outcome is wide open.

"Everything is possible," Le Pen told supporters on Thursday, while earlier in the week Macron warned his followers not to discount a Le Pen win.

"Look at what happened with Brexit, and so many other elections: what looked improbable actually happened," he said.