A Germanwings A320 aircraft has crashed in the French Alps.
Flight 4U 9525 was flying between Barcelona and Dusseldorf when it went into an eight-minute descent before coming down near the town of Digne at 1053 local time (0953 GMT).
There were 144 passengers and six crew members on board, including 67 Germans.
President François Hollande said: "The conditions of the accident, which have not yet been clarified, lead us to think there are no survivors."
The aircraft was 24 years old, Airbus confirmed.
Carsten Spohr, the chief executive of Lufthansa, which owns Germanwings, 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."
At a press conference this afternoon, Germanwings CEO Thomas Winkelmann said contact between the aircraft and French air traffic control was lost at 1053 when the plane was at an altitude of about 6,000 feet. It then crashed.
Winkelmann said the pilot had more than ten years experience with Lufthansa and Germanwings and had spent more than 6,000 hours flying Airbus aircraft.
The plane was last subject to a routine check in Dusseldorf yesterday. Its last routine inspection took place in summer 2013.
Germanwings said in a statement: "Flight 4U 9525 was a scheduled flight travelling from Barcelona to Dusseldorf. There were 142 passengers and six crew members registered on flight 4U 9525. At this point, no additional information is available.
"Germanwings is conducting a full investigation. Until it is completed, we are unable to provide any further details. Germanwings will issue regular updates whenever additional details become available."
A statement from Airbus said: "The aircraft involved in the accident... [was] delivered to Lufthansa from the production line in 1991. The aircraft had accumulated approximately 58,300 flight hours in some 46,700 flights."