The Paris office of the French satirical magazine Charlie Hebdo has been attacked by gunmen, killing at least 11 people. [Photo/Xinhua]

Masked gunman have attacked the Paris office of the French satirical magazine Charlie Hebdo, killing at least 12 people and wounding other 4 before escaping, reports say.

Ten staff at the magazine and two police officers were killed, including famous cartoonists Charb and Cabu, a reporter from the Le Monde said, citing a police source.

Witnesses spoke of sustained gunfire at the office as the attackers opened fire with assault rifles, according to media reports.

"Without doubt, it's a terrorist attack against an office that has been threatened several times, which is why it was protected," French president Francois Hollande said visiting the shooting scene.

"They will be hunted down and brought to justice," the president stressed.

France, the target of Islamist fighters in reprisal for its military strikes against Islamist strongholds in Iraq and the Sahel region, has aborted several terror attacks in recent weeks, Hollande said.

This is the deadliest terror attack in France in at least two decades. The country has raised its alert status for Paris to the highest level.

The satirical weekly has been under controversy in the past with its take on news and current affairs. The magazine was fire-bombed in November 2011 a day after it carried a caricature of the Prophet Muhammad.

Its latest tweet was a cartoon of the Islamic State militant group leader, Abu Bakr al-Baghdadi.

An emergency cabinet meeting is to be held at 14: 00 local time in Elysee.

Press offices, department stores, public transportation and places of worship in France will be placed under "reinforced protection", French Prime Minister's office announced.

The United States said it condemned the attack in the “strongest possible terms”.

“Everybody here at the White House are with the families of those who were killed or injured in this attack,” White House spokesman Josh Earnest said, speaking on MSNBC.

British Prime Minister David Cameron also condemned the attack and pledged solidarity with the French people against "all forms of terrorism."

"The murders in Paris are sickening. We stand with the French people in the fight against terror and defending the freedom of the press," Cameron said on his Twitter account.