French voters will pick a new president on Sunday, choosing between young centrist Emmanuel Macron and far-right leader Marine Le Pen in a watershed election for the country and Europe.
Polling day follows an unprecedented campaign marked by scandal, repeated surprises and a last-minute hacking attack on Macron, a 39-year-old who has never held elected office.
The run-off vote pits the pro-Europe, pro-business Macron against anti-immigration and anti-EU Le Pen, two radically different visions that underline a split in western democracies.
Le Pen, 48, 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.
Voting will begin on the mainland at 0600 GMT in 66,546 polling stations. Most will close at 1700 GMT, except those in big cities which will stay open an hour longer.
A first estimate of the results will be published around 1800 GMT.
The last polling showed Macron — winner of last month's election first round — with a widening lead of around 62 percent to 38 percent before hacking revelations on Friday evening. A campaigning blackout entered into force shortly after.
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."
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 on Saturday.
There has been no claim of responsibility for the French hack, but the government and Macron's team previously accused the Kremlin of trying to meddle in the election. However, Moscow denied the allegations.
Whoever wins Sunday's vote 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.
Macron would be France's youngest-ever leader and was a virtual unknown three years ago when he was named economy minister, the launching pad for his sensational presidential bid.
The ex-investment banker'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 fervently pro-European and wants to re-energise the 28-member European Union, following Britain's referendum vote last summer to leave.
But Le Pen is hoping to spring a shock that would resonate as widely as Britain's decision to withdraw from the EU or the unexpected triumph of US President Donald Trump.
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 vowed to reduce net immigration to 10,000 people a year, crack down on outsourcing by multinationals, lower the retirement age and introduce hardline measures to tackle Islamic extremists.