At least 20,000 people marched through the Belgian capital Brussels on Sunday in one of the biggest marches outside France in solidarity with the Paris terror attacks, officials said.

A huge "Brussels is Charlie" electronic sign in French, Flemish and English stood atop a city centre building as the march kicked off at about the same time as a massive rally in Paris, AFP reporters said.

People at the head of the march held banners saying "United against hate" and "Freedom of speech" and several young people draped themselves in the French flag.

Police and the mayor of Brussels both said at least 20,000 people attended.

The march was largely silent, with strains of French national anthem La Marseillaise ringing out.

Representatives from Muslim and Jewish associations took part in the rally.

Top Belgian cartoonist Philippe Gelluck also attended to show support for murdered colleagues from the French satirical magazine Charlie Hebdo.

"We have to fight on, like our parents and grandparents did, against religious fascism. I will continue more than ever, in honour of my fallen friends, and the idea of freedom," he said.

"I know the Muslim community feels wounded and humiliated by these cartoons, but they were not taking aim at Islam but at fundamentalism."

Meanwhile, twelve thousand people joined a rally in Vienna Sunday in honour of victims of the Islamist attacks in Paris, organisers said.

The rally, under the banner "Together against terrorism" was called by the Austrian government and religious communities.

In Luxembourg, around 2,000 people rallied outside the French embassy in a show of solidarity.

A minute of silence was followed by the singing of the Marseillaise and the Luxembourg national anthem and the EU anthem "Ode to Joy".

The European Union, which is based in Brussels, has meanwhile sent its top three officials to the march in Paris.

*This story was edited by Ahram Online.