PARIS (AFP) - French police were on Monday desperately trying to track down a gunman on the loose in Paris after a shooting at leftwing newspaper Liberation left a young photographer fighting for his life.

After fleeing the daily's office in the east of Paris, the shooter crossed the city to the La Defence business district, where he fired several shots outside the headquarters of the Societe Generale bank, Paris prosecutor Francois Molins said.

Police said they were also checking a statement by a car driver who claimed to have been briefly taken hostage by a gunman near La Defence and forced to drop him off close to the Champs-Elysees.

He then hijacked a car and forced the driver at gun-point to drop him off close to the Champs-Elysees, triggering a huge police operation in and around the French capital's most famous avenue.

Unconfirmed rumours that the man was armed with grenades as well as the hunting-style pump-action shotgun used in the two shootings swept Paris and there were fears he could seek refuge in the Metro, the city's underground train network.

Police said a 27-year-old man was in a critical state in a Paris hospital after being shot by the gunman.

Liberation said the victim had just arrived for his first day's freelance work at the newspaper, as an assistant on a photo-shoot for its supplement Next. He had suffered buckshot wounds to his stomach and chest, the paper said.

The gunman was still at large as night fell on the French capital seven hours later.

No one was injured in the shooting outside Societe Generale's main office, which took place 90 minutes after the attack at Liberation.

Police said that CCTV images of the shooter suggested he was the same man who had stormed into the Paris headquarters of news channel BFMTV on Friday.

In that incident, the gunman emptied several cartridges from his shotgun before warning a senior editor: "Next time, I will not miss you." Several hours after the shooting, Liberation's website was heavily disrupted by a cyber attack.

Francisco Alvarez witnessed Monday's shooting at La Defence.

"I saw this guy with a cap and a shotgun, a pump-action shotgun, in his hand," Alvarez told AFP. "I don't think he was necessarily targeting anyone, he shot in the air then into a window. The first shot shocked everyone into silence and then the second caused a general panic. Then he ran away down the steps to the street."

As news of the Liberation shooting broke, police were quickly deployed outside major media offices in Paris for fear of further attacks.

Liberation executive Nicolas Demorand said the shooting in the paper's entrance hall had left staff traumatised.

"When you have someone with a shotgun coming into a newspaper's offices in a democracy, it is very, very serious, whatever the mental state of the person," Mr Demorand told AFP.

"If papers and other media have to become bunkers, something has gone wrong in our society." Liberation journalist Anastasia Vecrin described the horrifying scene she was confronted with on what was otherwise a normal Monday morning.

"I was just arriving for work and I saw a man lying on the ground, holding his stomach and with blood everywhere," she told AFP.

"I met two of the reception staff who were completely white and who told me: 'We've just been shot at'."

Interior Minister Manuel Valls said that everything possible would be done to apprehend the shooter.

"This individual is on the run and he represents a real danger. We will do everything we can to arrest him," Mr Valls said.