A Germanwings Airbus A320 plane has crashed in the southern French Alps between Barcelonnette and Digne, French aviation officials and police have said.
German airline Germanwings is a subsidiary of Lufthansa.
Germanwings flight 4U 9525 had been en route from Barcelona to Duesseldorf with 144 passengers and six crew.
French President Francois Hollande said: “The conditions of the accident, which have not yet been clarified, lead us to think there are no survivors.”
He said the crash was a tragedy, adding that the area was very difficult to access.
President Francois Hollande later called German Chancellor Angela Merkel to express his sympathy, the French presidency said.
The plane issued a distress call at 10:47 local time, the French interior ministry said, although details have not been released.
Search-and-rescue teams are headed to the crash site at Meolans-Revels, said regional council head Eric Ciotti.
French PM Manuel Valls said he had sent Interior Minister Bernard Cazeneuve to the scene and a ministerial crisis cell had been set up to co-ordinate the incident.
The interior ministry said debris had been located at an altitude of 6,500ft.
Spokesman Pierre-Henry Brandet told BFM TV that it would be “an extremely long and extremely difficult” search-and-rescue operation because of the remoteness.
Lufthansa chief executive Carsten Spohr tweeted: “We do not yet know what has happened to flight 4U 9525. My deepest sympathy goes to the families and friends of our passengers and crew.
“If our fears are confirmed, this is a dark day for Lufthansa. We hope to find survivors.”
The Airbus A320 is a single-aisle passenger jet popular for short- and medium-haul flights.
Germanwings wrote on its website: “We must confirm to our deepest regret that Germanwings flight 4U 9525 from Barcelona to Dusseldorf has suffered an accident over the French Alps. The flight was being operated with an Airbus A320 aircraft, and was carrying 144 passengers and six crew members. Lufthansa and Germanwings have established a telephone hotline. The toll-free 0800 11 33 55 77 number is available to all the families of the passengers involved for care and assistance. Everyone at Germanwings and Lufthansa is deeply shocked and saddened by these events. Our thoughts and prayers are with the families and friends of the passengers and crew members.”
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