French President Francois Hollande said it was likely all passengers and crew on the Airbus A320 had perished in the crash.
“There are not thought to be any survivors,” the president told reporters after the disaster.
The plane was travelling from the Spanish coastal city of Barcelona to the German city of Duesseldorf when it went down in the Barcelonnette area, in southeeastern France.
The plane issued a distress call at 10:47 am (0947 GMT), sources said.
The airliner was carrying 142 passengers and six crew members.
The plane belonged to Germanwings, a low-cost affiliate of German airline Lufthansa. The single-aisle A320 typically seats 150 to 180 people.
According to foreign media, the crashed A320 is 24 years old and has been with the parent Lufthansa group since 1991, according to online database airfleets.net
Interior Minister Bernard Cazeneuve, who said debris from the plane had already been found, was heading to the scene.
Shares in Airbus, the European aerospace giant, slumped on news of the accident, down 1.77 percent to 58.94 euros at 1100 GMT after briefly sliding two percent. -AFP