Airline officials say confusion continues to surround the final moments of the Germanwings Airbus A320 that crashed in the French Alps on Tuesday morning.

All 150 passengers on board the plane are feared dead, as reports from the crash site suggest it could take “days” to recover the bodies of victims from an area of debris spanning kilometres.

President Francois Hollande has said there will be a full investigation into what caused the plane to plummet into the side of a mountain in a remote region 100 miles north of Nice, calling it “a tragedy on our soil”.

French Prime Minister Manuel Valls said that search teams had managed to land near the site but found no survivors, adding that there were no indications as to what caused the crash.

In pictures: Germanwings Airbus A320 plane crash Show all 66 1 /66 In pictures: Germanwings Airbus A320 plane crash In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Flowers are left in front of the monument in homage to the victims of Germanwings Flight 4U 9525 in Le Vernet, southeastern France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Andreas Lubitz was deemed ‘unsuitable for flight duties’ for a period of time during his training with Lufthansa and was receiving regular treatment for depression, sources have claimed as investigators focus their inquiry on his personal life and background In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash People believed to be relatives of the deceased crew on Germanwings flight 4U9525 comfort each other at a reception centre in Le Vernet, France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Rescue workers gather with friends and relatives of those killed onboard Germanwings flight 4U9525 at a reception centre in Le Vernet, France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Flags representing some of the nationalities of the victims are seen as family members and relatives gather near the crash site of an Airbus A320 in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash German and Spain flags symbolizing some of the nationalities of the victims are seen as family members and relatives gather for a ceremony in Le Vernet near the crash site of an Airbus A320 in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Flags symbolizing some of the nationalities of the victims, are seen near the memorial stele in Le Vernet during a ceremony to pay tribute to the victims of an Airbus A320 in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French gendarmes and investigators make their way through debris from wreckage on the mountainside at the crash site of an Airbus A320, near Seyne-les-Alpes In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French gendarmes and investigators work amongst the debris of the Airbus A320 at the site of the crash, near Seyne-les-Alpes, French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French gendarmes and investigators make their way through the debris of the Airbus A320 at the site of the crash near Seyne-les-Alpes, French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Wreckage of the Airbus A320 is seen at the site of the crash, near Seyne-les-Alpes, French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A body of a victim is evacuated by a French Gendarmerie rescue helicopter from the crash site of an Airbus A320, near Seyne-les-Alpes In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Rescue workers recover bodies of victims from the crash site of an Airbus A320, near Seyne-les-Alpes In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French military personnel work amongst the debris of the Airbus A320 at the site of the crash, near Seyne-les-Alpes, French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A helicopter of the French Gendarmerie flies over the crash site of the Germanwings Airbus A320 that crashed in the French Alps, above the town of Seyne-les-Alpes, southeastern France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Search and rescue workers make their way through debris at the crash site of the Germanwings Airbus A320 that crashed in the French Alps, above the town of Seyne-les-Alpes, southeastern France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Flowers and lit candles are placed on the ground in Cologne Bonn airport Reuters In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Victims’ relatives join carers outside the school gym in Seyne Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Lufthansa CEO Carsten Spohr, left, and Germanwings CEO Thomas Winkelmann arrive for a press conference near the Germanwings headquarters in Cologne, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Andreas Lubitz, the co-pilot that crashed the Germanwings Airbus A320 in the French Alps Facebook In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Buses loaded with relatives of victims are escorted after their arrival at Marseille airport, southern France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Family and relatives of the victims of the Germanwings plane crash in the Alps are taken on bus to the Prat airport from a hotel in Castelldefels in Barcelona, Spain, to take a Lufthansa flight to visit the crash site in Seyne les Alps in France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash An Airbus plane of German airline Lufthansa carrying onboard relatives of the Germanwings plane crash victims takes off from the Duesseldorf airport in Duesseldorf, western Germany, en route to Marseille In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A Germanwings employee places flowers in commemoration of the victims of the Germanwings plane crash in the French Alps, at the airport in Duesseldorf, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Members of German Government Chancellor Angela Merkel, Vice Chancellor and Economy Minister Sigmar Gabriel and Foreign Minister Frank-Walter Steinmeier, from right, hold a minute of silence to commemorate the victims of the Germanwings plane crash in the French Alps at the parliament Bundestag in Berlin, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Realtives of passengers of the Germanwings airliner that crashed in the French Alps leave the Gran Hotel Rey Don Jaime towards Barcelona El Prat airport where a lufthansa plane will fly to Marseille, in Barcelona, Spain In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Olivier Cousin (R), director of the mountain rescue team, which is responsible for the safety of the emergency workers on site, gives an interview in Seyne Les Alpes, France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Alpine climbers take off in a police helicopter in Seyne Les Alpes In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash German Chancellor Angela Merkel (L), French President Francois Hollande (C) and Spain's Prime Minister Mariano Rajoy pay respect to victims in front of the mountain in Seyne-les-Alpes, the day after the air crash of a Germanwings Airbus A320 In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A member of the search and rescue personnel stands at the crash site of the Germanwings Airbus A320 in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Search and rescue personnel at the crash site of the Germanwings Airbus A320 in the French Alps Reuters In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A sealed container holds black box from the German Airbus operated by Lufthansa's Germanwings budget Airbus A320 crash In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash The voice data recorder of the Germanwings jetliner that crashed in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash The voice data recorder of the Germanwings jetliner that crashed in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Germanwings employees cry as they place flowers and lit candles outside the company headquarters in Cologne Bonn airport In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A student who knew some of the German students involved in a crashed plane, reacts during a minute of silence in front of the council building in Llinars del Valles, near Barcelona, Spain In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Photograph of victims, flowers and candles stand outside the Joseph-Koenig-Gymnasium high school where pupils had gathered to pay tribute to 16 students and two teachers from the school who were on Germanwings flight 4U9525 that crashed yesterday in southern France on March 25, 2015 in Haltern, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Pupils gather at the Joseph-Koenig-Gymnasium high school to pay tribute to 16 students and two teachers from the school who were on Germanwings flight 4U9525 that crashed yesterday in southern France in Haltern, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Students gather in front of the Josef-König secondary school in Haltern am See, western Germany, where some of the Germanwings plane crash victims studied Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A Lufthansa employee signs in a condolence book in Frankfurt, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash The flags of (L-R) Aragon, Spain and the European Union are lowered to half-mast at the Regional Assembly of Aragon in Zaragoza, Spain, as a sign of respect for the victims of the German plane crash in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash The German and the European Union flags hang at half mast in memory of the victims of the plane crash in France in front of the Federal Chancellery in Berlin, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French President François Hollande with Spain’s King Felipe VI and Queen Letizia pay their respects to the victims of the German plane crash in the French Alps Reuters In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Debris from the Germanwings Airbus A320 at the crash site in the French Alps above the southeastern town of Seyne Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Search and rescue personnel at the crash site of the Germanwings Airbus A320 in the French Alps Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Wreckage and debris lie on the mountain slopes after the crash of the Germanwings Airbus A320 over the French Alps EPA In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Staff members of Germanwings and Lufthansa hold a candlelight vigil outside their headquarters in Cologne Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A photo provided by the French Gendarmerie shows the crash site in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A rescue helicopter from the French Gendarmerie flies over the French Alps, as day fades into night near to the crash site of the Airbus A320 Reuters In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A general view of the crash site of a Germanwings Airbus A320 in the French Alps above Seyne-les-Alpes is pictured in this photo provided by the French Gendarmerie In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Family members of people involved in a crashed plane arrives at the Barcelona airport in Spain AP/Emilio Morenatti In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Rescue helicopters from the French Gendarmerie and the Air Force are seen in front of the French Alps during a rescue operation near to the crash site Reuters In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A helicopter of the French National Gendarmerie is seen in Seyne, south-eastern France, near the site where a Germanwings Airbus A320 crashed in the French Alps ANNE-CHRISTINE POUJOULAT/AFP/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French emergency services workers (back) and members of the French gendarmerie gather in Seyne, south-eastern France, near the site where a Germanwings Airbus A320 crashed in the French Alps BORIS HORVAT/AFP/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash An helicopter of civil security services is seen in Seyne, south-eastern France, near the site where a Germanwings Airbus A320 crashed in the French Alps ANNE-CHRISTINE POUJOULAT/AFP/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Relatives of passangers of the Germanwings plane crashed in French Alps arrive escorted by police officer at Terminal 2 of Barcelona El Prat airport in Barcelona David Ramos/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Relatives of passangers of the Germanwings plane crashed in French Alps arrive at Terminal 2 of Barcelona El Prat airport in Barcelona, Spain David Ramos/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Relatives of passengers killed in Germanwings plane crash arrive at the airport in Duesseldorf, Germany AP/Frank Augstein In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Police escort a family member of an aircrash victim at Barcelona's El Prat airport LLUIS GENE/AFP/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French firefighters prepare to take-off in Digne-les-Bains for the crash site of an Airbus A320, in the French Alps REUTERS/Jean-Paul Pelissier In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A family member of a passenger killed in Germanwings plane crash reacts as he arrives at Barcelona's El Prat airport REUTERS/Albert Gea In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash People arrive at a holding area for friends and relatives of passengers on Germanwings flight 4U9525 from Barcelona to Dusseldorf at Dusseldorf International Airport in Dusseldorf, Germany Sascha Steinbach/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash People waiting for flight 4U 9525 are lead away by airport staff at the airport in Duesseldorf, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A relative (C) of passangers of the Germanwings plane crashed in French Alps arrives at the Terminal 2 of the Barcelona El Prat airport David Ramos/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A man who appears to have waited for the missing flight 4U 9525 reacts at the airport in Duesseldorf, Germany AP/Frank Augstein In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash epa04676936 A man looks at a monitor showing a map released on the webpage 'flightradar24 with the exact point where the radar signal of the crashed Airbus A320 aircraft operated by German budget airline 'Germanwings' went missing near Barcelonnette, in the department of Alpes-de-Haute-Provence, in Madrid, Spain EPA

Last moments of the plane

Speaking in Cologne, Germanwings CEO Thomas Winkelmann revealed that the plane began descending shortly after it reached cruising height following take-off from Barcelona airport.

10.01am CET Flight 4U 9525 takes off

10.44am Plane reaches cruising altitude

10.45am Plane begins unexplained descent

10.47am Air traffic controllers issue ‘third phase’ distress call

10.53am Radar and radio contact breaks off

A long descent

According to Mr Winkelmann, the plane started to descend very shortly after it reached its cruising altitude – and continued to do so for eight minutes until it crashed into the mountain at an altitude of some 5,000ft.

He said there was no explanation for why this descent from 38,000ft began, but said the 24-year-old plane was checked the day before the flight and that the captain on board was very experienced, with more than 10 years’ service and 6,000 hours of flying time.

Was there a distress signal?

France's aviation regulator has said that the plane “did not itself make a distress call” during its eight-minute descent from cruising altitude.

While Germanwings’ Mr Winkelmann said there was still some confusion as to whether a distress signal had been sent from the plane, the DGAC authority said that controllers on the ground issued the “distress” call – the third and most serious of three stages of alerts used to help coordinate rescue efforts when an aircraft is considered in difficulty.

“The combination of the loss of radio contact and the aircraft's descent which led the controller to implement the distress phase,” a spokesman said.

Why no word from the cockpit?

The fact that there was seemingly no distress signal issued by the pilots themselves does not necessarily tell us much about what was going on in the cockpit at the time.

Speaking in London, aviation expert Mary Schiavo told CNN that a sudden disaster that disabled the crew, like rapid decompression, was just one of a number of possible explanations.

“[The fact there was] no distress call would explain why the pilots didn’t turn back for other airports or veer from the course that was heading straight for the mountains,” she said.

“[But] with no distress call we don’t know what the pilots knew, what the plane was doing and we don’t know the emergency.

“There are a lot of different scenarios [that involve] no distress call and that explain why they continued to descend into the Alps,” she added.

Another analyst, David Soucie, told the broadcaster that the very act of putting out a distress signal takes some concentration and time and would not necessarily be “the priority” for pilots struggling with an emergency situation.

Did the plane crash in a storm?

UK meteorologists have said they expect bad weather to be ruled out as a cause for the crash at an early stage in the investigation.

Though it is mountainous, there were no significant storms reported in the area.

French emergency services workers (back) and members of the French gendarmerie gather in Seyne, south-eastern France, near the site where a Germanwings Airbus A320 crashed in the French Alps (BORIS HORVAT/AFP/Getty Images)

Dr Rob Thompson, from the University of Reading, told Sky News: "The weather conditions in the area of southern France where the crash is reported to have occurred look like nothing out of the ordinary for this time of year."

What about terrorism?

While there has been little word on the possibility that the crash could be a terror attack in France or Germany, the US has been quick to rule it out as a likely cause.