Three polls for the second-round runoff put Macron at the highest level since before the first round, with an average score of 55.83%, up more than a point from Friday and more than three points from an average of five polls before the first round.

Prime Minister Jean Castex, however, said it was too early to claim victory.

"The game is not done and dusted," Castex said on France Inter radio.

An Ipsos poll saw Macron winning 56.5% of the vote, up half a point from Friday and 3.5 points from April 8, two days before the vote in which Macron and Le Pen qualified for the second round.

Polls by Opinionway and Ifop, at 56% and 55% respectively, also showed Macron with his highest share of voting intentions since before the first-round vote on April 10.

Finance Minister Bruno Le Maire told Europe 1 radio that Le Pen would "hand France's sovereignty to Vladimir Putin and to Russia" if she was elected.

Le Pen has in the past voiced admiration for the Russian president and says she would pull France out of NATO's integrated military command.

Le Maire said a Le Pen victory would mean the end of French sovereignty, an alliance with Putin, a lack of NATO protection and severed ties with Germany.

In a campaign clip, Le Pen accused Macron and his allies of frightening citizens into voting against her.

"Macron, aware of his sombre prospects of winning a second term, has turned to ... blackmail by fear. Fear is the president's only remaining argument," she said.

Centrist Macron and Le Pen are seeking to attract voters who backed far-left leader Jean Luc Melenchon, after he came third in the first round with about 22% of the vote.

Melenchon's party has not given any voting instructions for the runoff but Melenchon has called on his followers not to vote for Le Pen.

In his first televised interview since the first round, Melenchon reiterated the call.

"You will make a colossal mistake if you vote for Mrs Le Pen. I don't tell you to vote for Macron, search inside your heads what's best, but don't do this," he told BFM TV.

Melenchon added that he would now focus on the legislative election this summer in order to form a left-wing majority and become the country's Prime Minister.

"I call on the French to elect me Prime Minister," Melenchon said, adding that he would be prepared to work with both Macron and Le Pen as presidents and that he had no clear preference between the two.

The Prime Minister in France, who is appointed by the president, has to control a majority in the National Assembly.

According to an Elabe poll also published on Tuesday, 42% of Melenchon's voters are now ready to give their vote to Macron, up 7% from last week.