A general view shows Hundreds of thousands of people gathering on the Place de la Republique to attend the solidarity march (Rassemblement Republicain) in the streets of Paris January 11, 2015.[Photo/Agencies]

"We're not going to let a little gang of hoodlums run our lives," said Fanny Appelbaum, 75, who said she lost two sisters and a brother in the Nazi concentration camp at Auschwitz. "Today, we are all one."

Zakaria Moumni, a 34-year-old Franco-Moroccan draped in the French flag, agreed: "I am here to show the terrorists they have not won - it is bringing people together of all religions."

Among many children brought along to the march, Loris Peres, 12, said: "For me this is paying respect to your loved ones, it's like family ... We did a lesson about this at school."

German Chancellor Angela Merkel, British Prime Minister David Cameron and Italy Prime Minister Matteo Renzi were among 44 foreign leaders marching with Hollande. U.N. Secretary-General Ban Ki-moon, Israel's Benjamin Netanyahu - who earlier encouraged French Jews to emigrate to Israel - and Palestinian President Mahmoud Abbas were also present.

"(The march) will be an unprecedented demonstration that will be go down in the history books," Prime Minister Manuel Valls said.

The official estimate on attendance is due to be announced later. A 1995 protest against planned welfare cuts brought some 500,000-800,000 people onto the streets of the capital, while a 2002 rally against the far-right National Front's then leader Jean-Marie Le Pen afer he got into the run-off of that year's presidential election drew 400,000-600,000.

Twelve people were killed in Wednesday's initial attack on Charlie Hebdo, a journal know for satirising religions and politicians. The attackers, two French-born brothers of Algerian origin, singled out the weekly for its publication of cartoons depicting and ridiculing the Prophet Mohammad.

All three gunmen were killed in what local commentators have called "France's 9/11", a reference to the September 2001 attacks on US targets by al-Qaida.