German prosecutors said on Thursday they believed the co-pilot who crashed a Germanwings plane in the French Alps last week had searched on a computer for ways to commit suicide shortly before the crash which killed 150 people.

In a statement, prosecutors in his home town of Duesseldorf they said the computer, found in his home, also showed searches on cockpit doors and safety precautions related to them.

They said Andreas Lubitz had also "looked for information on ways to commit suicide" in computer searches that took place between March 16 and 23, one day before the crash.

"On at least one day, the person had for several minutes undertaken searches related to cockpit doors and their safety precautions," it added.

The disclosure feeds into an acceleration of the multiple investigations into the crash of the German airliner as police in the French Alps said they had found the plane's second "black box" cockpit recorder.

"The second black box has been recovered. The prosecutor is going to make an announcement", a Gendarmerie officer said.

The Marseille prosecutor in charge of the case, Brice Robin, confirmed he was planning a news conference for later on Thursday.

Robin said last Friday that preliminary evidence from the cockpit voice recorder, which was quickly recovered from the scene, suggested 27-year-old Lubitz crashed the jet on purpose after barricading himself at the controls.

The second "black box", or Flight Data Recorder, contains hundreds of parameters taken from the Airbus A320.

The first box, which records pilot conversations, cockpit sounds and radio messages, was found hours after the crash.

There was no immediate word on the condition of the device, designed to withstand the force of a significant impact.

If intact, the data is expected to provide further detailed evidence including any commands from the co-pilot seat.

France's BEA air crash investigation authority, which is expected to decode the information as part of a parallel safety investigation, was not immediately available for comment.

Investigators are still trying to work out the motive for which Lubitz would take the controls of the A320, lock the door that was specially reinforced after 9/11 and apparently deliberately steer the aircraft into a mountainside.

German daily Bild reported on Thursday that Lubitz had allegedly lied to doctors, telling them he was on sick leave rather than flying commercial planes.

Germanwings parent Lufthansa has come under pressure to explain what it knew about his condition.

It said this week that when Lubitz resumed pilot training in 2009 he provided the flight school with medical documents showing he had gone through a "previous episode of severe depression".