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Faced with the most polarizing choice in decades, French voters were on Monday urged by leaders from across the political spectrum to coalesce behind political novice Emmanuel Macron instead of his far-right opponent in the upcoming runoff election.

The former presidential candidates from both the Conservative and the Socialist parties, as well as current President Francois Hollande, called on supporters to throw their support behind centrist Macron for the good of the republic. On May 7, Macron faces a showdown with Marine Le Pen of the hard-right National Front following Sunday's first-round ballot.

The scandal-ridden Conservative candidate François Fillon, who came in third place with 19.9 percent, according to the French Interior Ministry’s tally, immediately threw his support behind Macron when he conceded Sunday and condemned the nationalist right-wing views of Le Pen and the National Front.

"Extremism can only bring unhappiness and division to France," said Fillon. "There is no other choice than to vote against the far right. I will vote for Emmanuel Macron. I consider it my duty to tell you this frankly. It is up to you to reflect on what is best for your country, and for your children."

Socialist candidate Benoit Hamo — who came in fifth place with only 6.4 percent, the worst result for the party in years — also called on his supporters to back Macron and reject Le Pen in "the strongest possible way.”

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Notably, Jean-Luc Mélenchon, the far-left candidate who came in fourth place with 19.6 percent in Sunday’s election, has not endorsed Macron, but told his supporters to “vote with your conscience.”

"What is at stake is France's make-up, its unity, its membership of Europe and its place in the world"

Hollande, called for "solidarity" and "cohesion" among voters in support of his former protégé, Macron.

"The presence of the far-right in the second round is a risk for the country," Hollande said in a televised address from the Elysee palace. "What is at stake is France's make-up, its unity, its membership of Europe and its place in the world."

For the first time in French history, no mainstream candidate will be on the ballot in next month's second-round runoff — a huge defeat for the center-right and center-left groupings that have dominated the country's politics for decades.

The election also presents voters with the starkest possible choice: Macron's vision of a tolerant France and a united Europe with open borders against Le Pen's "French-first" platform that calls for closed borders, tougher security, less immigration and dropping the shared euro currency to return to the French franc.

A senior French Muslim leader called on the country's nearly 5 million Muslims to "vote massively" to elect Emmanuel Macron president. Dalil Boubakeur, rector of Paris' Grand Mosque, called the final May 7 vote to choose the next French head of state "decisive for the destiny of France and its religious minorities."

Emmanuel Macron arrives for a ceremony in memory of mass killings of Armenians by Ottoman forces in 1915, in Paris on Monday. Lionel Bonaventure / EPA

Macron, a political novice, won 23.8 percent in Sunday's first-round ballot and Le Pen gained 21.5 percent, according to the French Interior Ministry.

If Le Pen is defeated by a wide margin when French voters go to the polls for the runoff election on May 7 it will be déjà vu all over again for the National Front party and the Le Pen political dynasty.

Marine Le Pen’s father, Jean Mari Le Pen, founded the National Front political movement and brought it to its zenith in 2002 when he reached the second and final round of the presidential election.

But turned off by his far-right views, French voters flocked to the polls in the runoff to make sure he would not win, instead electing former President Jacques Chirac with a resounding 78 percent of the vote.

There have been calls for demonstrations against the National Front across France Monday evening in cities from Paris to Bordeaux and Grenoble.