Police moved in on the demonstrators, some of whom threw bottles and firecrackers, an AFP journalist saw. Three people were arrested, according to police.
Several hundred young people rallied in the Bastille square -- the historic site where the 1789 French Revolution began -- after projections suggested Le Pen would contest the second round against Emmanuel Macron, a centrist and former banker.
A protest leader called on the public through a loudspeaker to rally "against Marine and against Macron." "We have come here to protest against the pantomime of this election," a demonstrator told AFP.
Another "anti-fascist demonstration" also took place late Sunday in the western coastal city of Nantes.
Youth push over a glass bottle container during in Paris , Sunday April 23, 2017. (AAP) Source: AAP
Le Pen's father, Jean-Marie, scored the first breakthrough in the French presidential elections by the National Front, winning a slot in the runoff in the 2002 ballot.
He was routed in a head-to-head contest by the centre-right incumbent, Jacques Chirac.
Centrist Emmanuel Macron and far-right leader Marine Le Pen on Sunday emerged as the projected winners of a nail-biting first round presidential vote in France.
The likely result clears the way for a straight two-way fight between the pair in a second and final round on May 7, with opinion polls saying Macron is the favourite.
WATCH: Le Pen hailed result as 'historic'
Related reading
French election: Macron, Le Pen through to second round
