Marine Le Pen casts her vote in the first round of voting on Sunday - EPA

Polls have opened in the first round of France’s most unpredictable and high-stakes presidential election in decades, with far-Right leader Marine Le Pen and the maverick centrist Emmanuel Macron leading the field.

A Le Pen victory could lead to the collapse of the European Union, experts warn, but after the victory of Donald Trump in the US and the Brexit vote in the UK, most agree that there is no safe bet in the French race.

French Election - Latest Poll Average

Unprecedented security measures were in place to keep voters safe as they cast their ballots, with 50,000 police officers and 7,000 soldiers deployed across the country.

View photos A Femen activist wearing the mask of US president Donald Trump is detained as she demonstrates in Hénin-Beaumont, northern France, where far-Right leader and presidential candidate Marine Le Pen was votingCredit: AP More

Voting began just three days after a French jihadist shot dead a policeman on the Champs-Elysées in Paris, furthering pre-election jitters and pushing security and terror back to the top of the political agenda.

Islamic State of Iraq and the Levant (Isil) claimed the attack, as it has done for a series of assaults in France that began in early 2015 and have cost the lives of more than 230 people.

Profile | Emmanuel Macron

At a polling station in a primary school on Rue Martel in the trendy 10th arrondissement of Paris, there were no police on duty and no security checks.

Parisians doing their civic duty there before shopping for lunch said they were undeterred by terror threats.

"I'm 85 and I lived through the war and the Nazi occupation, so I'm not scared," said Gerard Samson, a retired film-maker.

Mr Samson said he had been a life-long supporter of the Socialist party but, as the Socialist candidate Benoit Hamon has little chance of getting elected, he was conflicted.

"This is the first time I have had to hesitate," he said, declining to say who he had plumped for.

French presidential election 2017 - in pictures

There are 11 candidates in the running for Sunday’s first round, including a pair of Trotskyists, three fringe nationalists, a former shepherd, and a man who wants to colonise Mars.

But there are just four who stand a chance of getting through to the run-off on May 7: Ms Le Pen, Mr Macron, the communist-backed firebrand Jean-Luc-Mélenchon, and the scandal-scarred conservative François Fillon.

The pair who will square off for the second round will be known at around 7pm UK time when usually accurate exit polls are announced.

View photos Francois Fillon, a member of Les Républicains political party of the French centre-Right, casts his voteCredit: Reuters More

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