PARIS, April 19 (CNA) - French Prime Minister Jean Castex said Tuesday (Apr 19) that his government would tender its resignation if Emmanuel Macron is re-elected president, in a bid to provide a "new impetus" for Macron's centrist party ahead of parliamentary elections in June.

Macron is facing a close race in the run-off on Sunday against far-right veteran Marine Le Pen, with analysts warning that low turnout could prove a wildcard even though most polls show Macron in the lead.

If he is re-elected, "in the subsequent days, as is the tradition, I will present the president with my resignation and that of the government," Castex told France Inter radio.

"I'm among those who think a new impetus should be found after the president's re-election," he added.

The parliamentary vote in June will be a further test of Macron's popularity, and renewing his majority will be essential for pursuing his reformist agenda, including an overhaul of the pensions system that would require most people to work longer before retiring.

There has been speculation that European Central Bank chief Christine Lagarde could be offered the post of prime minister, although she sidestepped a question on the issue at a press conference last week.

Macron and Le Pen will face off Wednesday evening in their first televised debate of the campaign, which could prove critical for winning over millions of voters, in particular on the left, who have told polling firms they remain undecided.

Opinion polls currently put the centrist Macron at 53 per cent to 56 per cent in the run-off against 44 per cent to 47 per cent for Le Pen, in a much tighter finish than in 2017, when the same candidates faced, off but Macron carried the vote with 66 per cent.

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 on Apr 10 with about 22 per cent of the vote.

Melenchon's party has given no voting instructions for the runoff after its internal consultations showed most people would abstain or submit a blank vote on Apr 24, adding to uncertainty over the outcome.

"The game isn't over yet and we certainly can't draw conclusions ... that this election, this match, is already decided," Castex said. "We have to convince the French that Emmanuel Macron's programmes are the best for France and for them."

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, after she previously voiced admiration for the Russian president.