Paris: Tens of thousands marched in Paris to support firebrand leftist presidential candidate Jean-Luc Melenchon, who has shaken up France's election campaign with a surprise jump in the polls.

Melenchon of the Left Front, who represents a coalition of leftist parties including the Communists, has emerged as a significant factor in the campaign just as Socialist frontrunner Francois Hollande faces a resurgent threat from incumbent President Nicolas Sarkozy.

His virulent attacks on the rich, France's elite and austerity measures have struck a chord with many voters, and polls this week showed him rising above the symbolic 10 percent mark, up four points from the start of the year, with only five weeks to go before the April 22 first round of voting.

Decrying a France "disfigured by inequality," Melenchon called for a "civic insurrection" as he addressed a sea of supporters in Place de la Bastille.

Waving red Left Front and Communist Party flags, tens of thousands of supporters marched through central Paris under cloudy skies in a symbolic rally to "retake the Bastille" -- the square where the medieval fortress and prison was stormed in the watershed event of the French Revolution.

Organisers said more than 100,000 people took part in the rally, held on the anniversary of the Paris Commune uprising of 1871.

"We have returned, the people of France's revolutions and rebellions. We are the red flag!" Melenchon roared to the crowd, saying the rally marked the start of a "citizens' revolution."

In a 20-minute speech, Melenchon outlined a programme focused on taxing the rich and financial world, boosting social spending and increasing workers' rights.

He also vowed constitutional changes enshrining the rights to abortion, to homosexual marriage and a "green rule" forcing France to protect the environment.

To chants of his name, Melenchon vowed to "open a new chapter" in France's history and offered support to the peoples of Greece, Spain, Portugal and Italy, who he said were "under the weight of oppression" from European austerity measures.

"We must today, in this France that has been disfigured by inequality ... refound the republic, refound France itself," he said, before his speech ended with the singing of left-wing anthem "The Internationale" and the French national anthem.