France's far-right candidate Marine Le Pen is closing the gap with President Emmanuel Macron ahead of the second round of the country's presidential election according to a new poll.

The OpinionWay-Kea Partners poll published by Les Echos and Radio Classique on Tuesday showed Le Pen narrowing the gap by one point as voter turnout continued to fall, although Macron would still win the run-off with 54 per cent of the vote.

The poll's turnout estimate further declined by 1 per cent to 70 per cent, down from 74.56 per cent in 2017, which was already the lowest since 1969. 

On Tuesday, conservative former president Nicolas Sarkozy said he would vote for centrist Emmanuel Macron in a run-off presidential vote against Marine Le Pen on April 24.

Sarkozy praised Macron's 'commitment to Europe' as being 'clear and unambiguous'.

'I will vote for Emmanuel Macron because I believe he has the necessary experience in the face of grave international crisis. His economic project puts the value of work as the top priority and his commitment to Europe is clear and unambigious,' Sarkozy said ahead of the second-round vote . 

'We must abandon our partisan habits... Fidelity to right-wing republican values and our governing culture must lead us to answer Emmanuel Macron's call for unity,' he said.

Le Pen, 53, secured a run-off against the president in the French elections after she received 23.15 per cent of the vote in the first round on Sunday, just four points behind Macron and the best-ever showing by a far-right party.