French voters are picking a new president, choosing between Emmanuel Macron, an independent centrist, and Marine Le Pen, the far-right leader, in an election crucial for both France and the European Union.
The battle for the top job at the Elysee Palace has been the most divisive in a generation.
Le Pen has portrayed the ballot as a contest between the "globalists" represented by her rival - those in favour of open trade, immigration and shared sovereignty - versus the "nationalists" who defend strong borders and national identities.
"The political choice the French people are going to make is clear," she said in her opening remarks during a heated debate between the pair on Wednesday night.
Polls opened on the mainland at 06:00 GMT on Sunday in 66,546 polling stations after a campaign marked by surprises and a hacking attack on Macron.
Voting at most polling stations will close at 17:00 GMT, except those in big cities, which will stay open an hour longer.
A first estimate of the results will be published at around 18:00 GMT.
Blandine, a French voter who did not provide her last name, said she voted for Le Pen "just to piss off people".
Speaking to Al Jazeera from the 10th arrondissement of Paris, Blandine explained she is "sick" of the mainstream political establishment. Although she doesn't expect Le Pen to win, Blandine voted for the far-right candidate "so her results are higher".
Daniel, another Le Pen voter, had just returned from attending a church service when he spoke to Al Jazeera. "If Macron wins, it will be very difficult for France," he said, accusing the centrist candidate of seeking to raise taxes and increase immigration.
"Le Pen is better than Macron for this country, of course," he said, adding: "I don't agree with everything she says."
Aka, a young man training to become a security guard, told Al Jazeera that while Macron was not his favorite candidate, he was planning to vote for him anyway "to oppose" Le Pen and her party's "racist comments".
"They are trying to mask their racism, but it is in their genes so it won't work. But anyway, the election is already over, Emmanuel Macron is going to win."
The last opinion poll showed Macron - winner of last month's election first round - with a widening lead of around 62 percent to 38 percent before the hacking revelations on Friday evening.
A campaigning blackout entered into force shortly afterwards.
Hundreds of thousands of emails and documents stolen from the Macron campaign were dumped online and then spread by anti-secrecy group WikiLeaks, leading the candidate to call it an attempt at "democratic destabilisation".
Kenneth Grey, a retired FBI special agent and lecturer at the University of New Haven, told Al Jazeera he is not surprised by the hacking attack.
"It certainly does seem to be the new way to try to affect politics in other countries," he said.
"Hack into their email, release the contents, and if there is embarrassing information there, it may very well cause a swing in the election."
Grey said that "unless there is a smoking gun within these emails", he does not believe it will have an effect on the election result.
France's election authority said publishing the documents could be a criminal offence , a warning heeded by traditional media organisations but flouted by Macron's opponents and far-right activists online.
"We knew that there were these risks during the presidential campaign because it happened elsewhere. Nothing will go without a response," French President Francois Hollande told AFP news agency on Saturday.
There has been no claim of responsibility for the French hack, but the government and Macron's team previously accused Russia of trying to meddle in the election - accusations denied in Moscow.
Whoever wins Sunday's vote it is set to cause profound change for France, the world's sixth-biggest economy, a permanent member of the UN Security Council and a global military power.
Winds of change
It is the first time neither of France's traditional parties has a candidate in the final round of the presidential election under the modern French republic, founded in 1958.
Rim-Sarah Alouane, a PhD candidate and researcher in public law at the University of Toulouse, says Le Pen "has already won" by "normalising a toxic nationalist, xenophobic and eurosceptic ideology".
"The possibility of having a far-right frontrunner as France’s next president should raise concerns, and many still do not realise the magnitude of this danger," she told Al Jazeera on Sunday.
Macron , a former investment banker, was a virtual unknown three years ago when he was named economy minister, the launch pad for his presidential bid.
He left Hollande's Socialist government in August and formed En Marche, a political movement he says in neither of the left or the right and which has attracted 250,000 members.
Macron's programme pledges to cut state spending, ease labour laws, boost education in deprived areas and extend new protections to the self-employed.
He is also staunchly pro-European and wants to re-energise the 28-member European Union, following Britain's referendum vote last summer to leave.
Rokhaya Diallo, a journalist and filmmaker, says the vote between Macron and Le Pen is emblematic of "a deep identity crisis" in France, which is "willing to get rid of the politicians who have been around forever".
"None of them represent the left, which shows how the general political landscape have been shifting to the right during the last for decades," Diallo told Al Jazeera on Sunday.
"Whether [Le Pen] wins or not, her victory stands in how her ideas especially regarding law and order are now acceptable."
"France is not a closed country. We are in Europe and in the world," Macron said during Wednesday's debate.
On her part, Le Pen is hoping to spring a surprise that would resonate as widely as Britain's decision to withdraw from the EU or the unexpected triumph of US President Donald Trump.
She sees herself as part of the same backlash against globalisation that has emerged as a powerful theme in the US and in recent ballots in Britain, Austria and the Netherlands.
She has pledged to organise a referendum on withdrawing France from the EU and wants to scrap the euro, which she has dubbed a "currency of bankers".
She has also pledged to reduce net immigration to 10,000 people a year, crack down on outsourcing by multinationals, lower the retirement age and introduce measures against what she calls Islamic extremists.
Many voters still see her party as anti-Semitic and racist despite her six-year drive to improve its image.
Macron topped the first round of the presidential election on April 23 with 24.01 percent, followed by Le Pen on 21.30 percent, in a crowded field of 11 candidates.
The results revealed Macron was favoured among wealthier , better educated citizens in cities, while Le Pen drew support in the countryside as well as poverty-hit areas in the south and rustbelt northeast.
Voting for the runoff started for French voters in North America and some overseas territories on Saturday.