Candidates in first TV debate

France's tumultuous presidential election battle steps up a gear as the main candidates face off in the first of several TV debates, gunning for every vote with just a month to go.

In France's most unpredictable election in years, far-right National Front leader Marine Le Pen and Emmanuel Macron have been running neck-and-neck for weeks, with the latest opinion poll showing the centrist just half a percentage point ahead for the first round of voting on April 23.

The debate will be an unprecedented chance for French voters to compare candidates before the first round as the frontrunners will share the stage with trailing candidates Francois Fillon of the right and Benoit Hamon of the left, along with the far left Jean-Luc Melenchon.

All 11 contenders, spanning the spectrum from Trotskyist left to the far right, will take part in another debate on April 4.

Advisors to 48-year-old Le Pen, who polls show would lose to Macron in the May 7 run-off if the election were held today, said she would tear into the "globalist" programme of her pro-EU rival.

The 39-year-old former economy minister will also come under pressure from Fillon, who will attempt to claw back votes lost to Macron since he became embroiled in a damaging fake jobs scandal.

Polls currently show Fillon, the one-time favourite, crashing out in the first round behind Le Pen and Macron, following revelations of payments by parliament to his wife and children as well as loans and lavish gifts from wealthy friends.

Two men representing the ailing left -- the Socialist Party's Hamon and Communist-backed radical Melenchon, currently fourth and fifth in the polls -- are also hoping to use Monday's three-hour television joust to sway millions of undecided voters.