Several thousand people gather to pay tribute to victims of a shooting by gunmen at the offices of the satirical weekly newspaper Charlie Hebdo during a demonstration in Marseille, January 10, 2015. French police searched for a female accomplice to militant Islamists behind deadly attacks on the satirical Charlie Hebdo weekly newspaper and a kosher supermarket and maintained a top-level anti-terrorist alert ahead of a Paris gathering with European leaders and demonstration set for Sunday. [Photo/Agencies]

PARIS -- A massive rally is planned for Sunday in Paris, where police are being deployed amid heightened security.

Dozens of world leaders including Britain, Germany, NATO and the Arab League will converge on the French capital in a show of defiance and unity after deadly shooting at a satirical magazine Charlie Hebdo and hostage-taking in a Jewish supermarket.

The march, which is to start at 3 pm (1400 GMT) and be made in silence, will reflect the profound shock felt in France and across the world over the worst Islamist assault on a European city in nine years.

Up to a million people are expected to attend Sunday's "cry for freedom" rally, according to the Guardian.

Security forces will be on the highest alert for the event, which will attended by about 40 heads of state and government.

German Chancellor Angela Merkel, British Prime Minister David Cameron and Italy Prime Minister Matteo Renzi will march with President Francois Hollande. Turkish Prime Minister Ahmet Davutoglu and Israel's Benjamin Netanyahu are also expected to take part.

Hundreds of thousands of people took to the street on Saturday in France's main cities after deadly shooting at a satirical magazine Charlie Hebdo and hostage-taking in a Jewish supermarket.

In a press conference, French Interior Minister Bernard Cazeneuve said 700,000 protestors took part in Saturday's rallies in French main cities of Toulouse, Lille, Marseille, Lyon, Grenoble and Clermont-Ferrand.

In Toulouse, where a young self-styled Islamist killed seven people including three kids in 2012, people did not wait for Sunday national rally to condemn terrorism and racism.

According to police data, 120,000 people were walking in the streets in the southern city.

In Nantes, the march drew 70,000 demonstrators, asking "to live together, free, equal and in solidarity".

About 30,000 people took to the street in Nice, a similar number in Marseille and 40,000 in Lille, north France, local reports said.

On the same day, hundreds of people holding pens aloft in support of free expression rallied in New York City to mourn victims of a deadly terror attack targeting a French satirical publication.

The demonstrators braved freezing temperatures in Manhattan's Washington Square Park as a woman danced under a sign that read "Je suis Charlie."

"I am Charlie" has emerged as a rallying cry since two shooters killed 12 people Wednesday at the Paris headquarters of the satirical magazine Charlie Hebdo. Organizers said they were showing solidarity with the French after three days of violence that, all told, left 20 dead, including three gunmen.