French President Francois Hollande called on voters to back centrist Emmanuel Macron in the second round of the presidential election, warning of dangerous consequences if far-right candidate Marine Le Pen were to win.

"The presence of the far-right in the second round is a risk for the country," Hollande said in a televised address.

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

He said he would vote for his former economy minister, because he was best placed to unite the people of France.