FRANKFURT (AFP) - The co-pilot of the Germanwings jet that crashed in the French Alps was on the job since September 2013 and had 630 hours of flying experience, the parent company, German flag carrier Lufthansa, said on Thursday.

The co-pilot "was First Officer at Germanwings since September 2013", a Lufthansa spokesman told AFP. He had been trained as a pilot at Lufthansa Flight Training in the northern German city of Bremen and had 630 hours of flying experience under his belt.

In comparison, the plane's pilot had more than 10 years experience and 6,000 hours of experience flying the Airbus A320 model, Lufthansa revealed previously.

The spokesman said Lufthansa could neither confirm nor deny information that said one of the two pilots on the doomed flight was locked out of the cockpit before the plane went down.

A source close to the investigation told AFP that cockpit recordings recovered from the crash site indicated one of the seats in the cockpit was pushed back and the door opened and closed.

Then knocking is heard, said the source, adding "there was no more conversation from that point until the crash".

The source said an alarm indicating the proximity to the ground could be heard before the moment of impact.

All those on board were killed when Germanwings flight 4U 9525 from Barcelona to Duesseldorf crashed in remote terrain on Tuesday, after an unexplained eight-minute descent in mid-flight.

No distress signal was sent from the Airbus A320 and the crew failed to respond to ground control's desperate attempts to make contact.

The cockpit recording showed the pilots speaking normally in German at the start of the flight, the source said, adding that it could not be determined if it was the captain or the first officer who left the cockpit.

The Lufthansa spokesman said "we have received no information so far about this" from the investigating authorities.

Germanwings also said it had no such information as yet.