An EgyptAir flight reported missing between Paris and Cairo has crashed, French President Francois Hollande confirmed.
The Airbus A320 with 66 people on board disappeared from radar at 02:30 Cairo time (00:30 GMT), soon after leaving Greek airspace.
Greece's defence minister says Flight MS804 made "sharp turns" and plunged before dropping off the radar.
A major search is under way in seas south of the Greek island of Karpathos.
Greek and Egyptian armed forces are involved in the effort, and France has offered to send boats and planes.