At least 12 people have been killed and several more seriously injured after armed gunmen stormed the Paris offices of French satirical magazine Charlie Hebdo.

The publication has previously been the target of a firebombing after publishing cartoons in 2011 joking about Muslim leaders.

Sources close to the investigation have been quoted as saying two men “armed with a Kalashnikov and a rocket-launcher” stormed the building in central Paris and “fire was exchanged with security forces.”

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French President Francois Hollande said there was “no doubt” the shooting was a terrorist attack of “exceptional barbarity”, and declared a national day of mourning on Thursday.

Twelve people were reportedly killed in the attack, with another four in critical condition. Reports suggest 10 of those killed were journalists at the paper, while another two were police officers.

After the shooting, the gunmen reportedly hijacked a car and knocked over a pedestrian as they sped away.

“About a half an hour ago two black-hooded men entered the building with Kalashnikovs (guns),” a witness told French iTELE TV News.

“A few minutes later we heard lots of shots,” he said, adding that the men were then seen fleeing the building.

A woman reads an issue of the French satirical weekly newspaper Charlie Hebdo. Photo: Getty

Charlie Hebdo has lampooned religious and public figures across Europe for 20 years.

The magazine gained notoriety in February 2006 when it reprinted cartoons of the Prophet Mohammed that had originally appeared in Danish newspaper Jyllands-Posten.

Its offices were fire-bombed in November 2011 when it published a cartoon of Mohammed and under the title “Charia Hebdo”. No one was injured in that attack.

French president Francois Hollande arrives at the scene. Photo: Getty

Despite being taken to court under anti-racism laws, the magazine continued to publish controversial cartoons of the Muslim prophet.

In September 2012 Charlie Hebdo published cartoons of a naked Mohammed as violent protests were taking place in several countries over a low-budget film, titled ‘Innocence of Muslims’, which was made in the United States and insulted the prophet.

French schools, consulates and cultural centres in 20 Muslim countries were briefly closed along with embassies for fear of retaliatory attacks.

Editor Stephane Charbonnier, who has received death threats and lives under police protection, has reportedly been killed in the attack.

Its latest tweet was a cartoon of the Islamic State militant group leader, Abu Bakr al-Baghdadi.

Charlie Hebdo’s website, which went offline during the attack, now reads “Je suis Charlie” (I am Charlie) on a black banner.

The hashtag “Je suis Charlie” has been trending on social media since the attack.

—with ABC, AAP