Video of the gunmen fleeing the attack has emerged.

People stand outside the French satirical newspaper Charlie Hebdo's office after the shooting.

Image source, AP

French politician Philip Cordery said a democratic freedom had been attacked: "Not only France, the whole of Europe is under shock today because by doing this horrendous act, the terrorists are once again attacking one of the important symbols of freedom, which is freedom of the press... and I think it's important for all democrats to unite and fight strongly against terrorism."

Fiamnetta Venner, who used to work at Charlie Hebdo, tells the BBC that journalists at the magazine had been afraid such an attack might happen: "We all were frightened of this moment, and this moment arrived. All of our friends who died, each day we will integrate them inside us. But I think they have just woken up an entire nation, because it's a generation of artists, of journalists who disappeared today."

French President Francois Hollande (centre left), flanked by Interior Minister Bernard Cazeneuve (right), walk outside the French satirical newspaper Charlie Hebdo's office in Paris.

Image source, AP

Echoing the language of other world leaders, Nato Secretary General Jens Stoltenberg called the attack "a barbaric act and an outrageous attack on press freedom".

More from Chancellor Merkel: "I'm shocked to receive the news of the malicious attack on a newspaper office in Paris. In these hours of pain I would like to express to you and your countrymen the sympathy of the German nation."

Some of the magazine's cartoonists are among the dead, Le Point has reported.

French police officers and forensic experts examine a car used by armed gunmen who stormed the Paris offices of satirical newspaper Charlie Hebdo.

Image source, AFP

The attackers went to the second floor of the Hebdo offices and started firing indiscriminately in the newsroom, Christophe DeLoire of Reporters Without Borders tells AP news agency. "This is the darkest day of the history of the French press," he said.

Italian President Matteo Renzi has added his voice to international condemnation of the attack, tweeting, external that "violence will always lose against freedom".

Chancellor Merkel said the shootings in France are not only an attack on French citizens, but on freedoms of the press and speech.

German Chancellor Angela Merkel has condemned the attack as "abominable".

French terrorism expert Jean Charles Brisard tells the BBC that the attack was well planned: "What we can say is, looking at the images and videos that are coming out, is the individuals were well-prepared, well-equipped; they had military-style weapons; they had probably bullet-proof jackets. So these individuals were well trained and determined indeed to commit this terrorist act, which is probably the worst that we've experienced in French history in the last 30 years."

Firemen at the scene of the attack on the Charlie Hebdo offices.

Image source, EPA

"I am profoundly shocked by this brutal and inhuman attack," European Union President Jean-Claude Juncker says.

BBC profile: Charlie Hebdo and its satirical role in French politics

The attack took place as staff held their weekly editorial media, a source has told the France 2 news channel.

@nilicule tweets, external: Saddened by the amount of anti-Islam commentary in my timeline. Terrorism is not an Islam problem, it's an extremism problem. #CharlieHebdo

France 24 TV is showing amateur footage apparently of the gunmen firing outside the building, running over to a person lying on the pavement and shooting at them while shouting slogans before getting into a car and driving off.