The Germanwings co-pilot who crashed an Airbus into the French Alps, killing all 150 aboard, told his ex-girlfriend that "one day everyone will know my name", according to German newspaper Bild.

In an interview, the 26-year-old flight attendant — identified only as Maria W — told Bild that when she heard about the crash she recalled Andreas Lubitz telling her last year: "One day I'm going to do something that will change the whole system, and everyone will know my name and remember."

French officials have said the black box voice recorder indicates that Lubitz, 27, locked his captain out of the cockpit on Tuesday and deliberately flew Flight 4U 9525 into a mountainside in what appears to have been a case of suicide and mass killing.

French prime minister Manuel Valls said all signs were "pointing towards an act that we can't describe: criminal, crazy, suicidal".

German prosecutors revealed searches of Lubitz's homes netted "medical documents that suggest an existing illness and appropriate medical treatment", including "torn-up and current sick leave notes, among them one covering the day of the crash".

They did not specify the illness.

According to Bild, the young woman, who was "very shocked", flew with Lubitz on European flights for five months last year, during which time they were believed to have been romantically involved.

Lubitz would awake screaming 'we're going down'

The woman said if Lubitz did deliberately crash the plane, "it is because he understood that because of his health problems, his big dream of a job at Lufthansa — as captain and as a long-haul pilot — was practically impossible".

"He never talked much about his illness, only that he was in psychiatric treatment," she said.

The pair separated "because it became increasingly clear that he had a problem", she told Bild, adding that at night he would wake up and scream "we're going down" and was plagued by nightmares.

Bild earlier reported that Lubitz sought psychiatric help for "a bout of serious depression" in 2009 and was still getting assistance from doctors, quoting documents from Germany's air transport regulator.

Lufthansa chief executive Carsten Spohr said Lubitz had suspended his pilot training, which began in 2008, "for a certain period" before restarting and qualifying for the Airbus A320 in 2013.

A French police chief said the personality of Lubitz was a "serious lead" in the inquiry but not the only one.

"We have a certain number of elements which allow us to make progress on this lead, which is a serious lead but which can't be the only one," police chief Jean-Pierre Michel said.

He said the investigation so far has not turned up a "particular element" in the life of Lubitz which could explain his alleged action.

Half of the 150 victims of Tuesday's disaster were German, with Spain accounting for at least 50 and the remainder composed of more than a dozen other nationalities.

Germanwings said Friday it had offered the victims' families "up to 50,000 euros ($70,300) per passenger" towards their immediate costs.

The assistance, which the families would not be required to pay back, was separate from the compensation that the airline will likely have to pay over the disaster, a Germanwings spokesman told AFP.

Germany to hold national memorial for victims

Germany will hold a national memorial ceremony and service for victims of the flight on April 17, regional authorities said.

The ceremony will be held at Cologne Cathedral in western Germany, a region from where many of the victims originated.

It is due to be attended by German chancellor Angela Merkel and president Joachim Gauck, a spokeswoman for the regional North Rhine-Westphalia government said.

Families and friends of the victims, as well as representatives from other countries affected by Tuesday's air disaster are invited, she said, adding they also wanted to enable anyone wishing to express their condolences to take part.

Mr Gauck attended a memorial service on Friday for 16 pupils and two teachers from a school in the western town of Haltern, who had been flying back from an exchange trip in Spain.

A religious ceremony also took place on Saturday morning (local time) in the French Alps town of Digne-les-Bains, police said.

Lubitz lived with his parents in his small home town of Montabaur in the Rhineland and kept an apartment in Dusseldorf, the city where his plane was bound from Barcelona.

Dusseldorf prosecutors said the evidence found in the two homes "backs up the suspicion" that Lubitz "hid his illness from his employer and his colleagues".

They said they had not found a suicide note, confession or anything pointing to a "political or religious" motive but added it would take "several days" to evaluate the rest of what was collected.

Reiner Kemmler, a psychologist who specialises in training pilots, noted that people "know that depression can compromise their airworthiness and they can hide it".

"If someone dissimulates — i.e. they don't want other people to notice — it's very, very difficult," Kemmler told Deutschlandfunk public radio.

Lubitz locked himself into the cockpit when the captain went out to use the toilet, then refused his colleague's increasingly desperate entreaties to reopen the door, French prosecutor Brice Robin said.

Captain 'tried to break through door with axe'

According to Bild, the captain even tried using an axe to hack through the armoured door as the plane was sent into its fatal descent by Lubitz.

The tragedy has prompted a shake-up of airline safety rules.

The European Aviation Safety Agency (EASA) recommended Friday that at least two people be present in the cockpit of planes at all times, which is the standard in the United States.

German authorities agreed to the rule for Lufthansa, its subsidiary Germanwings and other companies.

Investigators said Lubitz's intention was clear because he operated a button sending the plane into a plunge.

For the next eight minutes, Lubitz was apparently calm and breathing normally.

Recovery operations at the remote crash site were still ongoing, with French officials continuing to comb the mountain for body parts and evidence.

The plane's second black box, which records flight data, has not yet been recovered.

AFP