Andreas Lubitz rehearsed his plan to crash a Germanwings flight into the French Alps, killing 150 people, a report claims.

German newspaper Bild cites sources close to the investigation into the tragedy as saying Lubitz practised reducing flight altitude on the plane on its outbound flight from Dusseldorf to Barcelona on the same day as the actual crash.

According to the sources, an interim report from France's investigating agency is due to be published shortly and will refer to a "controlled descent that lasted for minutes and for which there was no aeronautical justification".

The co-pilot was known to have suffered from severe depression and had looked up ways of committing suicide in the days before the crash.

A search of his home following the crash found torn-up sick notes intended for his employer which showed he should not have been flying on the day of the crash.

Lufthansa, the owner of Germanwings, has refused to comment, saying the investigation is ongoing.

All 150 people died on the Airbus A320 crash as the plane flew back from Barcelona to Dusseldorf on March 24th.

Evidence from the recovered voice recorder suggests co-pilot Lubitz (27) deliberately locked flight captain Patrick Sondheimer out of the cockpit when he went for a toilet break and then put the plane into a steady descent.

The captain could be heard trying to smash through the cockpit door with an axe while shouting at Lubitz to open the door.

The plane took eight minutes to descend.