Two police officers are reported to be among the dead, as were cour of the paper's best-known cartoonists, who were known as Charb, Cabu, Wolinski and Tignous.
Visiting the site of the attack near Paris’s Place de la Bastille, President François Hollande said there was no doubt that the incident was a “terrorist attack” and condemned its “exceptional barbarity”.
“We will punish the attackers,” he declared promising to “pursue them for as long as is needed”.
Several attacks have been foiled in the last few weeks, Hollande told reporters, adding that “We knew we were threatened.”
Prime Minister Manuel Valls raised the terror alert in the Paris region to its highest level following the attack.
Two men with their faces concealed by balaclava helmets stormed the offices, opening fire with automatic weapons, reports said, with some saying they had a rocket-launcher.
They are reported to have escaped in a stolen vehicle and to have headed for the north-east of the city.
Its latest edition featured a cartoon of the Virgin Mary giving birth to Jesus Christ.
British Prime Minister David Cameron was quick to condemn the attack.
"I'm sure the whole House will want join me in condemning the barbaric attack this morning on an office of a magazine in Paris," he told the British parliament on Wednesday.