Paris, France - The last of French voters are casting their ballots in the first round of the presidential election, in a political event that could not only have significant consequences for the country but also the future of the European Union.

Polls close at 8pm local time, and results are expected soon after.

Four candidates in Sunday's election have a realistic chance of reaching the second round run-off on May 7, with just 5 percentage points separating them according to the latest opinion polls.

They are: Emmanuel Macron, a former minister and leader of the centrist En Marche! party; Marine Le Pen, president of the far-right National Front; Francois Fillon, a former minister and leader of the conservative Republican party; and Jean-Luc Melenchon, leader of the far-left La France Insoumise party.

At least two candidates, Le Pen and Melenchon, have promised to review the country's ties with the EU and raised the prospect of leaving the bloc.

However, the EU is not the only dividing line, with candidates holding sharply contrasting views on immigration, economic policy and the country's Muslim population.

Le Pen has promised to halt immigration and strengthen the country's borders, while her centrist rival Macron supports the open-door policies of German Chancellor Angela Merkel, which have allowed more than a million refugees and migrants from the Middle East into Europe.

On economic policy, Macron favours cuts to public spending, as does his conservative competitor, Fillon.

Melenchon on the other hand wants a 100 percent tax on earnings above $429,000 a year.

Security will also be a concern, as France has experienced a number of attacks by supporters of the Islamic State of Iraq and the Levant (ISIL) group.

Most recently, a police officer was shot to death and two others injured on Paris' Champs Elysees in an attack on Thursday evening that was also claimed by ISIL, also known as ISIS.

As a result, up to 50,000 police and 7,000 soldiers have been deployed across the country on Sunday to secure the 66,546 polling stations.

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Before official campaigning had ended on Friday, candidates were battling not just against each other but also against the apathy that has taken hold among large sections of the French population.

Incumbent President Francois Hollande decided not to stand because of his low poll numbers, and Benoit Hamon, the candidate for Hollande's Socialist party, trails way behind the four frontrunners.

Nina Wardleworth, teaching fellow in French at the University of Leeds, told Al Jazeera the race was tight for "a number of reasons".

"It is unprecedented for an incumbent president not to stand again, so the Socialist Party was thrown into disarray," she said, adding that Hamon was a rushed choice. "There is therefore no traditional left-right battle between the two main parties this year."

Wardleworth described Macron as an "astute political operator" who managed to captalise on widespread disillusionment, while Le Pen's electoral success was bolstered by "recent terrorist attacks".

Polling companies put the number of those planning not to vote or to cast blank ballots at nearly 30 percent, with many others, half the electorate according to some estimates, undecided about who to vote for.

Voters in French South American and Caribbean territories, including Guiana and Martinique, went to the polls on Saturday, a day before voting in mainland France.

According to the interior ministry, voter turnout by 15:00 GMT Sunday was 69.42 percent - only slightly lower than in 2012, when turnout in the same hour was 70.59 percent.

The final abstention rate was also similar to levels seen in the previous presidential election at around 20 percent, according to surveys by Harris Interactive and CNews.

Jean Edouard, a taxi driver, told Al Jazeera that he was supporting Macron out of fear of both Le Pen and Melenchon.

"Le Pen for her closeness to racist views but also Melenchon because he acts like people are not able to think by themselves," he said.

Many of those who told Al Jazeera they would not be voting for any candidate said their decision was based on a general distrust of politicians, a feeling shared even by some of those who have decided on a candidate.

Speaking to Al Jazeera before Sunday's election, Jeanie, a pensioner from Paris, said that she would vote for Fillon despite the corruption scandal that has engulfed his campaign.

"When we vote in France, we do so reluctantly," she said next to her husband who pinched his nose as he gestured dropping a ballot into a box.

Follow Shafik Mandhai on Twitter: @ShafikFM