France's two presidential candidates go on the offensive in crucial debate
The far right's Marine Le Pen brands her opponent a "candidate of the elite"
Centrist Emmanuel Macron strikes back, accusing her of lying
The two argue over terrorism, the French economy and Europe
Four days from the poll, the debate is seen as the last real chance for Le Pen to close the gap on Macron in the polls
The last time the far right came this close to power was in 2002 under Marine Le Pen's father, Jean-Marie Le Pen
Some 20 million French viewers are expected to tune in for the debate, due to last 2 hours and 20 minutes
The centrist has quickly become combative.
He has accused his opponent of "lies", of complaining about all that goes wrong but proposing nothing as a solution and of saying "stupid things".
But he has also been on the defensive, denying he was responsible for the sale of big French companies while a minister in President Hollande's government, which Le Pen said was "not in the interests of France".
There was a wrangle over the directing of the debate, with Macron asking for cutaways and Le Pen's camp preferring otherwise, RTL reports, external.
The use of cutaways will see cameras focusing on the candidate who is not speaking to show audiences their reactions.
In the past, candidates have used the time when their opponents were speaking to check their notes.
The TV directors said they would use cutaways "moderately", RTL said.
Here are the candidates just before the debate began.
Image source, AFPLe Pen starts with a smile, by linking Macron firmly to President Hollande's administration, which she says has been "catastrophic" for the country. She accuses him of having no economic patriotism.
France is the only big EU country that has failed to tackle unemployment, says Macron.
He says the solution is to give small- and medium-sized companies the opportunity to create more jobs and be more flexible.
The candidates are being asked about their policies. Here is what we know already:
Macron wants to:
Image source, Getty ImagesQuote MessageThere is a feeling of rage, an incomprehension of the way things work, of a Europe that no longer protects and a globalisation with too many losers
Le Pen wants to:
Image source, PAQuote MessageI think the euro is dead
Marine Le Pen
Macron opens with a broadside against his opponent.
He accuses her of being cloaked in a "spirit of defeat", of saying to the electorate that "globalisation is too hard".
By contrast, he says his vision is to revive the spirit of "French conquest".
Yes, is the short answer.
After the Brexit vote in the UK and the election of US President Donald Trump, France is the latest country to deal a blow to politics as usual.
Will the French people go for a pro-European liberal who has never before been elected, or a far-right challenger to the establishment, who has vowed to take on globalisation and France's relationship with the EU?
The candidates are asked how they are feeling before the election. Le Pen goes first and she is straight off the on the attack, presenting Macron as the establishment candidate.
She presents herself as the one who will be protecting the country, including its borders.
The debate has begun, with an introduction by the hosts.
"I expect... that it will demonstrate that Mr Macron and I have two radically different visions," Le Pen said as she arrived at the studios of France 2, wearing a blue jacket and white blouse, AFP news agency reports.
Both the candidates have now entered the venue.
Debate host Christophe Jakubyszyn has posted a photo of himself and fellow moderator Nathalie Saint-Cricq in the studio ahead of the debate.
"The pressure is mounting - but we are ready," he writes.
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In office for five years, he or she would wield significant power - including control of the armed forces and choosing the prime minister. The BBC's Karin Giannone explains.
How powerful is the French president?
Days before the deciding round, he told the BBC that the EU must reform or face the prospect of "Frexit".
Quote MessageMy mandate... will be to reform in depth the European Union and our European project
Emmanuel Macron says EU must reform or face Frexit
Security may be top of voters' minds, but there is always an economic context that will feature as a major consideration, argues the BBC's Andrew Walker.
Image source, AFPHe says he hopes the debate will provide a "moment of clarification" allowing him to explain his policies in detail and "show that Ms Le Pen's project is not up to the challenges facing France".
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She had her political awakening early - aged eight, says the BBC's Hugh Schofield. Is she about to reach the epitome of French power on Sunday?
Between the two rounds of the French election, she has been identifying herself with France and Frenchness.
Read what she stands for here.
Image source, EPAMarine Le Pen is equating herself with France: "Choose France" her campaign motto says
To fight the second round, and appeal to a broader electorate, Le Pen stood aside as leader of the National Front (FN). It was a symbolic act intended to show her concerns were for the country as a whole and not for her party.
When her father, FN founder Jean-Marie Le Pen, reached the second round in 2002, he polled just 18% against Jacques Chirac of the centre-right. Opinion polls for this contest suggest his daughter could more than double that score even if she loses on Sunday.
Macron has consistently led - but nothing is being taken for granted.
Check where the contenders stand in this BBC poll tracker.
