Pro-Europe centrist Emmanuel Macron vowed Sunday to battle the "threat of nationalists" after projected results showed he would face far-right leader Marine Le Pen in the run-off of France's presidential election next month.

"I want to be the president of the patriots against the threat of nationalists," the 39-year-old former banker told hundreds of flag-waving supporters.

"In your name, I will be... the voice of hope for our country and for Europe," said Macron, who had never before stood for election and only started his centrist movement 12 months ago.

He will meet Le Pen in the May 7 second round, according to the projections.

Opinion polls released after the first-round showed the pro-business moderniser would easily beat Le Pen, who has hardened her anti-immigration and anti-Europe rhetoric over the last week.

The French vote on Sunday was being closely watched as a bellwether for populist sentiment following the election of Donald Trump as US President and Britain's vote to leave the EU.