French President Emmanuel Macron will take his hunt for extra votes to the industrial heartlands of northern France on Monday, a blue-collar stronghold of his far-right rival Marine Le Pen who he will face in an April 24 presidential runoff vote.

Macron and Le Pen came out on top in Sunday's first-round vote, setting up a repeat of the 2017 duel pitting a pro-European economic liberal against a euro-sceptic nationalist.

Polls predict a close-fought second round with one survey projecting Macron will win with just 51% of the vote and 49% for Le Pen. The gap is so tight that victory either way is within the margin of error.

"Let's make no mistake, nothing has been decided yet," Macron told his cheering supporters after partial results showed him qualifying for the runoff.

He took aim at his far-right rival over the financing of her populist economic agenda that would see the retirement age cut to 60 for those who start work before 20, income tax scrapped for the under-30s and VAT on energy reduced to 5.5% from 20%.

Speaking of his own manifesto, Macron said: "Do you want a France that speaks of full employment and is serious about financing its welfare state, its pensioners, its schools, hospitals and public services?"

Macron supporters and some of his campaign insiders have said he must now focus on wooing the left.

Le Pen won 33% of the votes in the northern Hauts-de-France region. Left-wing candidates won a combined 27-28% of the vote in the area. How the left's votes are redistributed nationally will be a key factor in the second-round vote's outcome.

Le Pen has patiently detoxified the image of her far-right party and brought it closer to the mainstream at a time France has also lurched to the right in the wake of Islamist attacks. Even so, her softer, less combative manner belies a hardline anti-immigrant programme.

But it has been her focus on the cost-of-living issues troubling millions that has helped her tap into a widespread discontent towards rulers as she has toured towns and villages across France.

She said voters were making a choice between two opposite visions of France: "one of division, injustice and disorder imposed by Emmanuel Macron for the benefit of a few, the other a rallying together of French people around social justice and protection."

The yield on French 5- and 10-year government bonds hit multi-year highs ahead of the first round as the race tightened.

Morgan Stanley said in a briefing note that it expected spreads between French and German 10-year bonds to "hover close to the current level until the outcome of the second round".