The French presidential race has been jolted after long-time conservative frontrunner Francois Fillon became embroiled in revelations his wife drew hundreds of thousands of euros in salary as his parliamentary assistant amid suspicions she never actually worked.

And an incident at the Louvre museum on Friday, where a man with two machetes was shot after attacking a group of soldiers, has shifted the focus onto Le Pen's preferred subjects of security, Islam and immigration.

Polls have shown for months that she will win enough votes on April 23 to reach the second round runoff on May 7, but they also currently show that a mainstream candidate will beat her at that stage.

"French people on the whole share our vision of the country, the themes which are ours: the patriotism on which our project is built, and then the defence of our civilisation," she said on Saturday.

France was "undoubtedly at a crossroads where tomorrow we might not recognise our country any more", she said. 

She will address supporters at 1400 GMT in the city where she once compared the sight of Muslims praying in the street to the Nazi occupation.  

Sources in her party say up to 10,000 people are expected, although the room was only half full on the first day of the rally on Saturday.

The election had long been seen as a two-horse race between Le Pen and Fillon, but his expenses scandal has further boosted the chances of 39-year-old centrist independent Emmanuel Macron.

"On paper, Macron has the strongest chance of winning," one of Le Pen's advisors conceded on Saturday, speaking on condition of anonymity.

A former economy minister under unpopular Socialist President Francois Hollande, Macron is also running as a candidate outside the political establishment and has founded his own movement, En Marche (On The Move).

Benefiting from being a fresh face in a familiar field of characters, the pro-European moderate packed out a 8,000-place venue also in Lyon on Saturday and had thousands more watching on a big screen outside.

Macron said Le Pen "did not speak in the name of the people" and he took aim at nepotism in the FN, which was founded by her father, anti-Semitic former paratrooper Jean-Marie Le Pen.

Marine's 27-year-old niece, the hardline Marion Marechal-Le Pen, is also a senior figure in the party.

Among the key proposals in Le Pen's "commitments" to the nation is a pledge to hold a referendum soon after taking power on whether France should remain in the European Union.

She favours a radically overhauled EU which would repatriate almost all powers over economic policy, currencies and border control to member states.

She also proposes "zero tolerance" of crime, 15,000 extra police, imposing higher taxes on foreign workers and imports, as well as freeing small firms from red tape.

On economic policy, she wants to lower the retirement age and increase some welfare payments in an agenda designed to appeal to hard-pressed areas suffering from job losses.