Promoted by a spontaneous social media campaign, the London vigil begins at 1800 GMT.

A Facebook page launched in solidarity with the victims and their families describes the vigils as “Peaceful gathering[s] in support of Charlie Hebdo, Freedom of press and peace.”

“Against all forms of hatred, the defense of freedom of expression and peaceful tribute to the memory of the victims will be the only two unique demands of this rally."

#jesuischarlie Trafalgar Square #C4Newshttps://t.co/OZxGx5NWDb

— Oz Katerji (@OzKaterji) January 7, 2015

“We are Charlie and we are united.”

Organisers of the Trafalgar Square vigil have asked people to bring signs reading “JE SUIS CHARLIE” and drawings from Charlie Hebdo.

Crowds starting to gather for the #JeSuisCharlie vigil in Trafalgar Square #C4Newshttp://ift.tt/1425WOA

— Oz Katerji (@OzKaterji) January 7, 2015

People are also encouraged to bring flowers and pens “to celebrate freedom of expression.”

They have asked people not to bring candles for security reasons.

Participants have been asked to meet at the North Terrace in Trafalgar Square.

Journalists in Paris organized a similar event in Place de la Republique which started at 6pm local time.