More than 50,000 police and gendarmes were deployed to protect 66,000 polling stations for today's election, which comes just three days after a deadly attack on Paris's famed Champs-Elysees Avenue in which a police officer and a gunman were slain. Another 7,000 soldiers are on patrol.
The presidential poll is the first ever to be held while France is under a state of emergency, put in place since the November 2015 attacks in Paris left 130 people dead.
"We really need a change in this country, with all the difficulties we are facing and terrorism," Paris resident Alain Richaud said as he waited to cast his vote.
"There have been surprises (this year), there have always been scandals," said Le Touquet resident Pierre-Antoine Guilluy.
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Opinion polls point to a tight race among the four leading contenders vying to advance to the May 7 presidential runoff, when the top two candidates will go head to head.
France's 10 percent unemployment, its lackluster economy and security issues topped concerns for the country's 47 million eligible voters.
Voter Marie-Christine Colrat lamented: "Listen, too many candidates. And candidates that caused us a lot of problems, I think that's not a good thing for France."
Both Le Pen and Melenchon from opposite extremes of the political spectrum have supported pulling France out of the 28-nation bloc and its shared euro currency in a so-called "Frexit."
A French exit, however, could spark a death spiral for the EU, for France and Germany are the bloc's strongest economies and biggest proponents of a united Europe.
If either Le Pen or Melenchon wins a spot in the runoff, it will be seen as a victory for the rising wave of populism reflected by the votes for Brexit in Britain and Donald Trump in the United States.
The sun glistened across most of France today as voters and candidates cast their ballots. France's Interior Ministry said voter turnout at midday was 28.54 percent slightly stronger than it was in 2012, when turnout was high.
In the northern town of Henin-Beaumont, several activists from the feminist group Femen were arrested after staging a topless protest against the far-right Le Pen. Police intervened and stopped the commotion minutes before the candidate arrived to cast her ballot. No one was hurt.
Melenchon voted in Paris, as did Fillon.
But Fillon's wife, the scandal-hit Penelope Fillon, was conspicuously absent from her husband's side and voted 250 kilometers (155 miles) away near their 14th century manor house in Sarthe. She is facing preliminary charges for her role in the fake jobs scandal that has rocked her husband's presidential campaign.
Hollande, the current president, voted in his political fiefdom of Tulle in Correze, southwestern France. Political campaigning was banned from midnight Friday hours ahead of polls opening in France's far-flung overseas territories such as Guadeloupe, French Polynesia and French Guiana, which all voted Saturday.
The interminable queue that lasted several hours was caused by lack of polling stations - only one was set up for the estimated 57,000 registered French voters in Canada's most populous French-speaking city.
One retired American in Paris urged her neighbors to make their voices count.
"I think that it's important that every French voter gets out and votes today ... Did you see what happened in the United States? The same could happen here," said Renette Decicco, a 78-year-old out shopping for food.