The execution of a police officer is among the horrific scenes captured in a string of videos posted online in the aftermath of the Paris newspaper massacre.

Clips recorded by eye-witnesses on smartphones showed two masked gunmen dressed in black firing what appear to be rifles as terrified onlookers fled.

One video circulated on Facebook shows the two gunmen stood next to a Black Citroen car firing at distance as a police officer stood on the pavement of a tree-lined boulevard.

The camera then pans to show the officer, now wounded, on the floor clutching his leg and raising his arms in an apparent gesture of surrender.

The assailants march towards him before one shoots him casually in the head at close range. The officer's body immediately goes limp, while the gunmen run back to the car and drive off.

Images of the aftermath of the shooting showed the windscreen of a police car riddled with bullet holes and casualties being carried away on stretchers.

In footage filmed from a nearby rooftop one of the attackers can be heard shouting "Allahu Akbar" - meaning God is the greatest.

The gunmen were filmed running across the street outside the magazine office.

The clip, posted by journalist Martin Boudot, shows the gunmen firing a volley of shots before getting into a black car.

The narrator is heard to say "they're leaving now", seconds after shots ring out.

"Shush, they're there, they're there," a man replies quickly, before shouting and another volley of gunfire is heard.

The streets around Charlie Hebdo's offices are largely deserted in the footage but in another video a female pedestrian can be seen running and then crouching next to a car as a string of shots ring out

There were reports that some of the gruesome footage was aired by European broadcasters, while several clips were removed from social media sites within minutes of appearing.