- France votes today for its most unpredictable presidential election
- Polling to take place amid tight security after Paris' shooting incident
- The election is crucial for the future of the deeply divided country
The shooting on Paris's world-renowned Champs Elysees avenue on Thursday thrust questions of security to the fore of campaigning after nine months of relative calm.
On Saturday, police arrested a man brandishing a knife at Paris's Gare du Nord station, briefly causing panic as some passengers rushed out of the way.
France goes to the polls on Sunday in an election seen as crucial for the future of a deeply divided country and the beleaguered European Union.
Nearly a quarter of voters are still undecided, and surveys showed until now that the French are more concerned about jobs and the economy than terrorism.
But analysts warned the policeman's shooting could shift opinions, perhaps handing an advantage to candidates seen as taking a hard line on security, such as far-right leader Marine Le Pen.
In the aftermath of the attack, she called for France to "immediately" take back control of its borders from the European Union and deport all foreigners on a terror watchlist.
'Don't give in to fear'
Le Pen and 39-year-old centrist former banker Emmanuel Macron are leading the polls but the race has tightened in the final days and any one of four candidates could reach the runoff on May 7.
Conservative Francois Fillon and hard-left firebrand Jean-Luc Melenchon have fought it out for third place in the campaign, just a few points behind Le Pen and Macron.
In the wake of the shooting, authorities in Paris have offered additional guards for hundreds of polling stations in the capital, which will come on top of an already major security plan across the country.
"An extra guard or reinforcement of staff will be provided to any polling station that needs it," Paris town hall official Colombe Brossel said.
Around 50,000 police and 7,000 soldiers will be deployed to protect voters around the country.
The killing of policeman Xavier Jugele by 39-year-old gunman Karim Cheurfi on the Champs Elysees was the latest in a string of terror attacks in France that began in 2015. More than 230 people have been killed.
US President Donald Trump tweeted that he thought the attack in Paris "will have a big effect" on the election.
Adelaide Zulfikarpasic of BVA pollsters said: "If it were to benefit someone that would clearly be Marine Le Pen who has dominated this issue throughout the campaign, or Francois Fillon."
Le Pen moved quickly to present herself as the strongest defender against Islamist extremists.
"This war against us is ceaseless and merciless," she said, accusing the Socialist government of a "cowardly" response to the threat.
In an angry response, Prime Minister Bernard Cazeneuve accused Le Pen of attempting to exploit the killing, "as she does after every tragedy".
Fillon, the 63-year-old former prime minister who has stressed his previous experience, promised an "iron-fisted" approach to Islamic terror, saying: "Some haven't taken the full measure of the evil".
Macron, a 39-year-old moderate whom Fillon has portrayed as too inexperienced for the top job, said France was paying the price for intelligence service cuts made when he was premier between 2007 and 2012.
Describing the Champs Elysees shooting as an attack on democracy, Macron urged voters: "Do not give in to fear."
Communist-backed Melenchon, 65, was the only one of the four not to cancel his final campaign event on Friday. He called for a "Europe of rebels", during a rally in Paris with Pablo Iglesias, the head of Spain's far-left Podemos party.
"Several Europes are possible, it doesn't have to be just their Europe," said Melenchon, a eurosceptic who has pledged to renegotiate treaties with the bloc.
Voting began on Saturday in many of France's overseas territories such as Martinique and Guadeloupe in the Caribbean, and French citizens cast ballots in the US.
A BVA poll conducted on Thursday and Friday showed Le Pen and Macron tied on 23 percent, ahead of Melenchon with 19.5 percent and Fillon on 19 percent.
Though the race has four main contenders, a total of 11 are in the running, most in single digits.
14 years in prison
A clearer picture, meanwhile, has emerged of the violent past of the gunman in the Champs Elysees shooting.
Cheurfi was arrested in February on suspicion of plotting to kill police officers but released because of a lack of evidence.
A serial offender, he spent nearly 14 years in prison for a range of crimes including attacks on the police. He had shown "no signs of radicalisation" while in custody, said France's anti-terrorism prosecutor Francois Molins.
The shooting came days after two men were arrested in Marseille on suspicion of planning an imminent attack and follows a series of deadly strikes around Europe in the past month, targeting Stockholm, London and the Saint Petersburg metro.