A city-wide manhunt is underway for a gunman who opened fire at the reception of the Paris building of left-wing newspaper Libération, seriously injuring a photographer.
He is later believed to have opened fire at a second building, and carjacked a terrified man near the Champs-Elysées.
Police said the man was carrying a saw-off shotgun, and carrying a black sports bag loaded with grenades.
The alleged perpetrator entered the lobby of the newspaper on Monday, around 10:15am, and opened fire before fleeing.
The photographer's assistant, aged 27, is in a serious condition, shot in the chest and stomach, Liberation reported.
Le Parisien has tweeted a picture of the alleged gunman:
Shots were also fired Monday morning by a man outside the headquarters of the Société Générale at La Défense, HuffPost France reported, but no-one has been injured. The SG confirmed the reports of the shooting on its Twitter account.
A 65-year-old driver claimed to have been taken hostage by the gunman, and forced to drive him to the Arc de Triomphe, which is at the top of the Champs Elysées, according to BFMTV.
A police helicopter is tracking the alleged perpetrator, with French media reporting the gunman has been riding the Paris Metro after the attack.
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In a statement, President Francois Hollande said he had "been distressed to hear of the attack of the newspaper Libération's headquarters, in which a photographer assistant was seriously wounded.
"The head of state has asked the Minister of the Interior to urgently mobilise all means to stop the perpetrator or perpetrators," l'Elysée said.
The assistant had arrived at the building for a photo shoot for the magazine Next, HuffPost France said.
Police have cordoned off the area around the newspaper, on the Rue Beranger, and the scene is attended by the Police Commissioner Bernard Boucault.
French TV channel I-Tele reported the suspect was "40-45 years, a stout man with a hat hiding a shaved head, [wearing a] khaki coat."
Jean-Paul Sartre co-founded Libération. Imagine what he'd have made of a gunman opening fire on its staff.— Peter Allen (@peterallenparis) November 18, 2013
Fabrice Rousselot, managing editor of Libération, said all the staff at the newspaper were "extremely emotional" and expressed outrage that an individual could decide to "go after the press."
"We are horrified to witness this tragedy. In a democracy, it is very, very serious to decide to enter the offices of a newspaper with a gun, regardless of the mental state of the person," the editor of the newspaper Demorand Nicolas, told AFP.
"If newspapers and media have to become bunkers, that is something is wrong in our society."
Paris police have organised armed protection for several other French media organisations.
Police are heavily present along the Champs-Elysées, though the city's main shopping avenue has not been cordoned off.
On Friday an armed man broke into the Paris offices of news channel BFMTV, but did not fire any shots and no-one was injured, according to the BBC.
The suspect in that incident is said to have told witnesses "Next time I won't miss you," according to a police source cited in Libération.