An Airbus A320 airliner has crashed in the French Alps between Barcelonnette and Digne, French aviation officials and police have said.
The jet belongs to the German airline Germanwings, a subsidiary of Lufthansa.
The plane had reportedly been en route from Barcelona to Dusseldorf and was carrying 142 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."
Mr Hollande said the crash was a tragedy and called for solidarity with the victims, adding that the area was very difficult to access.
He said he would be speaking shortly with German Chancellor Angela Merkel.
The plane issued a distress call at 10:47 (09:47 GMT), according to sources quoted by AFP news agency.
Search-and-rescue teams are headed to the crash site at Meolans-Revels, said regional council head Eric Ciotti.
French Prime Minister Manuel Valls said he had sent Interior Minister Bernard Cazeneuve to the scene and a ministerial crisis cell to co-ordinate the incident had been set up.
The interior ministry said debris had been located at an altitude of 2,000 metres.
Both Airbus and Germanwings have said they are aware of the reports but cannot yet confirm them.
The Airbus A320 is single-aisle passenger jet popular for short- and medium-haul flights.