UPDATED 8.51pm: The co-pilot of the doomed Germanwings flight appears to have "deliberately" crashed the plane into the French Alps after locking his captain out of the cockpit, French officials say.

MORE: Cockpit doors locked since 9/11

But they do not believe he was part of a terrorist plot.

In a chilling account of the last minutes of Germanwings Flight 4U 9525, lead prosecutor Brice Robin on Thursday said 28-year-old Andreas Lubitz initiated the plane's descent while alone at the controls.

The young German appeared to "show a desire to want to destroy" the plane, Robin told reporters, basing his findings on sound recordings from the Airbus A320's cockpit flight recorder in the minutes before the crash that killed all 150 passengers and crew on board.

Friends say Lubitz never appeared anything but thrilled to have landed a job with the airline Germanwings.

Klaus Radca was a colleague at the local flying club, and can't believe what's happened.

"I got to know him as a very nice man. He was fun, a polite young man. I can't imagine it, I just can't imagine it."

A team of investigators have entered his parents' home and could be seen emerging with blue bags, a big cardboard box and what looked like a large computer.

The world aviation body says pilots must have regular mental and physical check-ups in the wake of the crash.

It says all pilots are required to undergo a periodic medical examination by a doctor who is trained in aviation medicine.

If there is any concern from this medical screening then a further, more specialised, assessment can be undertaken.

Airlines and aviation regulators are also changing their practices to ensure there are always two people in the cockpit at any one time.

Canada has ordered its airlines to post two people at all times in cockpits of passenger planes, effective immediately. 

Germany's aviation association has also announced it plans to introduce a two-person cockpit rule.

Among the dead in Tuesday's crash were Australian nurse Carol Friday and her son Greig, both from Melbourne.

Robin said those on board died "instantly" and probably were not aware until the "very last moment" of the impending disaster.

"The screams are heard only in the last moments before the impact," said the prosecutor.
"The co-pilot was alone at the controls," he said. "He ... refused to open the door of the cockpit to the pilot."

The pilot, believed to have gone to the toilet, made increasingly furious attempts to re-enter the cockpit, banging on the door, the recordings show.

There was no immediate clue as to the motive of the co-pilot, but investigators appeared to rule out terrorism.

"At this moment, there is no indication that this is an act of terrorism," Robin said, adding that Lubitz had no known terrorist connection.

Germany's interior minister echoed this, saying there was so far no indication of "a terrorist background."

Robin also said he was unwilling to use the word "suicide" and could not guess at Lubitz's motive.

"Usually when you commit suicide, you do it alone. When you're responsible for 150 people, I don't call that a suicide," he said.

The co-pilot, who deliberately set the controls "to accelerate the plane's descent" into the side of a mountain, "was conscious until the moment of impact," Robin said.

"This action can only be deliberate. It would be impossible to turn the button by mistake. If you passed out and leaned over on it, it would only go a quarter-turn and do nothing," he stressed.

"He didn't reply to a thing. He didn't say a word. In the cockpit, it was utter silence."

Lufthansa chief executive Carsten Spohr said he was "stunned" by the revelations and had "no indication" on the motives of Lubitz.

He added that no security "system in the world" could have prevented the co-pilot's actions.

Spohr said Lubitz had passed all psychological tests required for training and underwent regular physical examinations.

The shocking new information was released as families and friends of victims travelled to the remote mountainous crash site area.

Two planes arrived in southern France on Thursday from Barcelona and Duesseldorf with families and friends.

Tents were set up for them to give DNA samples to start the process of identifying the bodies of loved ones, at least 51 of whom were Spaniards and at least 72 Germans.

Meanwhile, the remains of victims, found scattered across the scree-covered slopes, were being taken by helicopter to nearby Seyne-les-Alpes, a source close to the investigation told AFP.