Witnesses spoke of sustained gunfire at the office as the attackers opened fire with assault rifles.
The satirical weekly has courted controversy in the past with its take on news and current affairs.
Its latest tweet was a cartoon of the Islamic State militant group leader, Abu Bakr al-Baghdadi.
An eyewitness, Benoit Bringer, told French TV channel Itele: "Two black-hooded men entered the building with Kalashnikovs. A few minutes later we heard lots of shots."
The men were then seen fleeing the building.
"It`s carnage," French police official Luc Poignant told another French channel, BFMTV.
Gunmen have attacked the Paris office of French satirical magazine
07 January 2015
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Gunmen have attacked the Paris office of French satirical magazine Charlie Hebdo, killing 10 people, French prosecutors say.
