France on Saturday prepared to choose between centrist President Emmanuel Macron and far-right challenger Marine Le Pen to rule the country for the next five years after a bitterly contested and polarising election campaign.

Macron is the favourite to win re-election in the run-off ballot on Sunday, and there are indications he bolstered his advantage with a combative performance in the one-off election debate against a somewhat defensive Le Pen this week.

But the president and his allies have insisted over the last week that nothing is in the bag, with a strong turnout crucial to avoid a shock in France comparable to the 2016 polls that led to Brexit in Britain and Donald Trump's election in the United States.

Polls in mainland France will open at 0600 GMT on Sunday and close 12 hours later, immediately followed by projections that usually predict the result with a degree of accuracy.

But voters in French overseas territories that span the globe and are home to almost three million people have already started voting.

Macron is the favourite to win re-election on Sunday and there are indications he bolstered his advantage with his debate performance
Macron is the favourite to win re-election on Sunday and there are indications he bolstered his advantage with his debate performance AFP / Ludovic MARIN

The first vote in the election was cast by a 90-year-old man in the tiny island territory of Saint Pierre and Miquelon off the northern coast of Canada.

Polls subsequently opened in France's islands in the Caribbean and the South American territory of French Guiana and voting later starts in territories in the Pacific and then in the Indian Ocean before it gets underway on the mainland.

Some 48.7 million French are eligible to vote.

Le Pen has insisted she will prove the polls suggesting Macron has the lead to be wrong
Le Pen has insisted she will prove the polls suggesting Macron has the lead to be wrong AFP / DENIS CHARLET

A Le Pen victory would send shockwaves across Europe. Left-leaning EU leaders including German Chancellor Olaf Scholz have pleaded with France to choose Macron over his rival.

The stakes are huge -- Le Pen would become modern France's first far-right leader and first female president. Macron would be the first French president to win re-election in two decades.

If elected, Macron is expected to address supporters on the Champ de Mars in central Paris at the foot of the Eiffel Tower.

Macron and Le Pen threw themselves into a final flurry of campaigning Friday, firing off attacks in interviews before last-minute walkabouts and rallies.

Le Pen insisted that opinion polls giving Macron the lead would be proved wrong and took aim at her rival's plan to push back the retirement age to 65 from 62.

Macron and his wife Brigitte took a walk on the beach at le Touquet, northern France, on the eve of the vote
Macron and his wife Brigitte took a walk on the beach at le Touquet, northern France, on the eve of the vote AFP / Ludovic MARIN

Macron for his part said Le Pen was trying to mask an authoritarian "extreme right" platform that stigmatises Muslims with a plan to outlaw headscarves in public.

But the campaign also had some lighter moments. Macron's quizzical stares during the TV debate and a daringly unbuttoned shirt during a campaigning break that provided a glimpse of his strikingly hairy chest became instant Internet memes.

Polls have shown Macron with a lead of some 10 percentage points. The highly anticipated TV debate on Wednesday did not change the trend and, if anything, allowed Macron to open more of a gap.

But the result is predicted to be closer than in 2017, when the same candidates faced off and Macron carried the day with 66 percent to 34 percent.

Analysts say abstention rates could reach 26 to 28 percent, with reluctant left-wingers needing to back the president for him to be sure of victory, although the 1969 record for a second-round abstention rate of 31.1 percent is not expected to be beaten.

Far-left leader Jean-Luc Melenchon, who scored a close third-place finish in the first-round vote on April 10, has pointedly refused to urge his millions of followers to back Macron while insisting they must not cast a single vote for Le Pen.

According to Martial Foucault, director of the Cevipof political studies centre, the greater the abstention rate the more the gap will narrow between Macron and Le Pen, describing this as a "real risk" for the president.

Early turnout indications will be closely watched from the overseas territories, where average incomes are lower than in mainland France and which generally backed Melenchon in the first round.

For Sandy Doro, an 18-year-old student at a polling station in French Guiana's capital Cayenne, voting "is an essential right that must be exercised".

Lyvio Francius, a student of the same age, was also voting for the first time but with less enthusiasm: "It was my mother who persuaded me and took me, otherwise I'm not interested, not really."

French nationals were also voting in the United States.

But even before the results are in, eyes are already turning towards the legislative elections which will in June follow hot on the heels of the presidential elections.