French President Francoise Hollande said 11 people had been killed while four others were critically injured. He said 40 people had been taken to safety.
The Chief of Paris police, Xavier Castaing, also said 11 people have been confirmed killed in the shooting.
Some of those killed were journalists, and at least two police personnel also died in the attack, officials said.
The attackers remained at large after fleeing the scene.
French news channel, France Info, quoted a witness, Benoît Bringer, who said he watched the attack from a nearby building.
“About a half an hour ago, two black-hooded men entered the building with Kalashnikovs. A few minutes later, we heard lots of shots,” Mr. Bringer said.
Mr. Bringer told the station that he saw the hooded men fleeing the building soon after.
President Hollande who alongside French Interior Minister, said the incident was “undoubtedly a terrorist attack of exceptional barbarity” and ordered that the country’s terrorist alert status level to be increased to the highest level.
He said several terrorist attacks have been prevented recently. Security has been increased in places of worship, news organisations and transport stations, which are often targeted by terrorists.
Charlie Hebdo’s tweet appeared to tease the leader of the Islamic State militant group, ISIS.
In the past, the newspaper stirred outrage among some Muslims after it published a satire of Prophet Muhammad and Islam.
In 2011 its offices were firebombed after it published a cartoon of the prophet on its cover promising “100 lashes if you don’t die laughing!”