The co-pilot of the doomed Germanwings flight deliberately crashed the plane into the French Alps after locking his captain out of the cockpit, but is not believed to be part of a terrorist plot, French officials said on Thursday.

The 28-year-old co-pilot deliberately initiated the plane's descent, Marseille prosecutor Brice Robin told a news conference.

Robin disclosed details of recordings made by the Airbus A320 cockpit flight recorder in the final minutes before the crash that killed all 150 aboard.