Marignane (France) (AFP) - The co-pilot of the doomed Germanwings flight appears to have "deliberately" crashed the plane after locking his captain out of the cockpit, French officials said Thursday, in revelations that sparked global shock and prompted some airlines to review their cockpit policies.

In a chilling account of the final minutes of Germanwings Flight 4U 9525, lead prosecutor Brice Robin said 28-year-old German Andreas Lubitz initiated the plane's descent Tuesday into the French Alps while alone at the controls.

Lubitz appeared to "show a desire to want to destroy" the plane, Robin told reporters after his team analysed the Airbus A320's cockpit voice recorder.

The first officer, who was described by neighbours and fellow flying club members as a "friendly" guy-next-door type who enjoyed jogging with his girlfriend, was not however believed to be part of a terrorist plot, officials said.

In an initial reaction, German Chancellor Angela Merkel said the findings added an "absolutely unimaginable dimension" to the tragedy in which 150 people were killed, mostly German and Spanish nationals.

Spain's Prime Minister Mariano Rajoy said he was "deeply shaken" by the news and sent his "heartfelt affection" to the victims' families, dozens of whom had arrived near the crash site.

The French prosecutor said the passengers were killed "instantly" by the crash and were probably unaware of the impending disaster until the "very last moment."

"The screams are heard only in the last instants before the impact," he said.

"The co-pilot was alone at the controls," he said. "[He] deliberately 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 appear to show.





- Controls set to 'accelerate' descent -





The French prosecutor downplayed the likelihood of Lubitz accidentally taking the plane down with an involuntary turn of the descent button.

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"If you passed out and leaned over on it, it would only go a quarter-way and do nothing," Robin said, adding Lubitz, who had worked for Lufthansa since 2013, had set the controls to "accelerate the plane's descent."

The co-pilot's motive remains a mystery.

"At this moment, there is no indication that this is an act of terrorism," Robin said, an assessment echoed by Germany's Interior Minister Thomas de Maiziere.

The search for clues saw investigators Thursday search Lubitz's home in the western town of Montabaur, where he lived with his parents, as well as the flat he kept for work in the Germanwings hub of Duesseldorf.





- 'Worst nightmares' -





A "stunned" Lufthansa chief executive Carsten Spohr said there wasn't "the slightest indication what might have led" to the Lubitz's actions.

The second-in-command had passed all psychological tests required for training, Spohr told a press conference, insisting: "He was 100-percent airworthy".

In the northwestern town of Haltern, which lost 16 students and two teachers killed while returning from a school exchange, the revelations about the cockpit lockout caused shock and anger.

"It's bad enough for the families to learn of the death of loved ones in an accident. But when it's clear that an individual may possibly have deliberately caused the accident, it takes on an even worse dimension," mayor Bodo Klimpel said.

The shaken principal of the stricken school, Ulrich Wessel, expressed anger "that a suicide can lead to the deaths of 149 other people."





- Changes to cockpit policy -





In the first industry responses to the disaster, Canada ordered its airlines to have two people in cockpits at all times, effective immediately. British low-cost carrier easyJet, Scandinavia's Norwegian Air Shuttle and Icelandair all made similar announcements.

Many US airlines already have such a policy in place.

Meanwhile, families and friends of victims gathered near the remote mountainous crash site area in the French Alps, where locals have opened their doors in a show of solidarity.

"We're all pitching in of course. There's no such thing as nationality, no such thing as religion," said one local volunteer, Charles Lanta.

Two Lufthansa planes transported the victims' loved ones to France from Barcelona and Duesseldorf.

Tents were set up for them to give DNA samples to start the process of identifying the remains of the victims, at least 50 of whom were Spaniards and at least 75 Germans.

Officials and police kept the media at bay to ensure their privacy.

They were briefed by the prosecutor, who said they reacted with "shock" to the findings.

Remains 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.

Policeman Xavier Vialenc said his officers "were trying to gather everything they could" but the operation would be "long, very long, at least a fortnight."

The crash site, which is situated at about 1,500 metres (5,000 feet) altitude, is accessible only by helicopter or an arduous hike on foot.

French President Francois Hollande and Merkel flew over the site Wednesday.

It was the deadliest air crash on the French mainland since 1974 when a Turkish Airlines plane crashed, killing 346 people.

Lufthansa said the aircraft was carrying citizens of 18 countries. Three Americans and three Britons were confirmed among the victims. The dead also included two babies.

A second black box, which records flight data, has not yet been recovered.