The co-pilot of the Germanwings flight which crashed into the French Alps appears to have deliberately crashed the plane.

German pilot Andreas Lubitz, 28, is said to have locked the captain out of the cockpit, before sending the plane into a descent as crew furiously banged on the door.

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Marseille prosecutor Brice Robin said Mr Lubitz’s actions could “only be deliberate” but said there was no indication it was an act of terorrism, and refused to describe it as suicide.

“I repeat, when he was alone, in charge of the Airbus, the co-pilot started the flight monitoring system to get the plane to descend,” Mr Robin said.

“The action on this altitude selector can only be voluntary, I repeat action on this altitude selector can only be deliberate.”

The plane disintegrated on impact. Photo: Getty

The recording showed the pilot and co-pilot talked normally and “courteously” for the first 20 minutes of the flight after it took off from Barcelona.

Mr Lubitz was left in control of the Airbus A320 after the captain left the cockpit to go to the bathroom, but refused to re-open the door for his colleague.

“One can then hear several calls from the commander asking to be allowed into the cockpit,” Mr Robin said of the cockpit audio recordings.

“He knocked on the door and there was no answer from the co-pilot either,” he said.

Mr Lubitz can allegedly be heard breathing calmly within the cockpit right until the final impact, which means he would have been alive.

“We can analyse it that the intention was to destroy this plane.”

Mr Robin said passengers could be heard screaming just before impact, but would have died instantly.

Australians Carol Friday and son Greig were on board.

“When we have the lives of 150 passengers involved, I can’t call this a suicide,” he said.

Mr Lubitz had worked at Germanwings since September 2013 and had more than 600 hours of flying experience.

According to parent company Lufthansa, the plane’s captain had more than 10 years experience and 10,000 hours flying the Airbus A320 model.

He has still not been named.

Investigators have searched both of Mr Lubitz’s home in Germany, with News Corp reporting authorities are likely to treat the crash as a mass murder investigation.

Lufthansa chief executive, Carsten Spohr said he was “stunned” by the revelations, but insisted their pilot screening process was adequate.

A French emergency worker at the crash site. Photo: AAP

“What has happened here is a tragic individual event,” Mr Spohr said.

“We are trying to deal with an enigma.”

“In a company that prides itself on its safety record, this is a shock. We select cockpit personnel carefully.”

Other budget airlines have responded to the Germanwings crash by introducing a two pilot rule which requires two pilots to be in the cockpit at all times.

In a statement, Germanwings said it still had “full faith” in its pilots.

“They remain the best in the world; this event is an extremely tragic isolated incident.”

“We share in the sadness, shock and incomprehension of the bereaved families and friends and that of millions of other people.”

We are shaken by the upsetting statements of the French authorities. 1/3

— Germanwings (@germanwings) March 26, 2015

Our thoughts and prayers continue to be with the families and friends of the victims. 2/3

— Germanwings (@germanwings) March 26, 2015