France Info radio also said police had confirmed a toll of 10 dead and five injured. Reuters had no immediate official confirmation of deaths.
The news channel quoted a witness as saying he saw the incident from a building nearby in the heart of the French capital.
"About a half an hour ago two black-hooded men entered the building with Kalashnikovs (guns)," Benoit Bringer told the station. "A few minutes later we heard lots of shots," he said, adding that the men were then seen fleeing the building.
A police official, Luc Poignant, said he was aware of one journalist dead and several injured, including three police officers.
"It's carnage," Poignant told BFM TV.
A firebomb attack gutted the headquarters of Charlie Hebdo in November 2011 after it put an image of the Prophet Mohammad on its cover.
© Thomson Reuters 2015