A gunman who has gone on the run in central Paris after two shootings is believed to be hiding in Metro Line 1 to evade police and according to reports is carrying live grenades.

The man was described as appearing "calm and determined", aged in his 40s, with a shaved head and wearing a long green coat and bullet-proof vest. Police said he was "of European type".

Police sources told Rue89 news site that the man was armed with grenades as well as a hunting rifle.

A helicopter flew over the Champs-Elysées following reports that the man had taken a driver hostage west of Paris and forced him to drive to the city's main thoroughfare. The driver dropped him outside the luxury hotel Georges V just off the Champs-Elysées.

The gunman entered the Liberation office shortly before 09.15am GMT, armed with a hunting rifle, and fired two shots before fleeing. A 27-year-old photographer's assistant was hit in the thorax and the stomach and was reported to be in critical condition.

It was believed to be the victim's first day at work.

Interior minister Manuel Valls said the shooting incident was a "scene of war that has nothing to do with democracy or the press".

"As long as this person is still on the loose and we do not know the motives, this represents a threat," Valls said. "We must move fast."

French president François Hollande said he had ordered "all possible means" to find the attacker.

After the Liberation shooting, the gunman fired shots in the air outside the headquarters of French bank Societe Generale in the La Defense business district.

The Liberation shooting came three days after a man broke into the Paris HQ of business channel BFMTV and fired several bullets before escaping. No-one was wounded in the incident but the gunman warned a senior editor: "Next time, I will not miss you."

According to authorities, the man was caught on CCTV and appears to be the same as the supsect in today's shootings.

Police have put a number of Paris offices of news organisations such as Le Parisien, Le Monde, les Echos and le Figaro and Europe 1 radio under guard.