An Egyptair flight from Paris to Cairo has been reported missing by the airline.
French President Francois Holland said in a statement that "all information gathered so far" indicates that the flight crashed.
In tweets published from Egyptair's official account, it said:
"An informed source at EGYPTAIR reported that EGYPTAIR Flight No MS 804 has lost communication with radar tracking system at 0245 (CLT)"
"EGYPTAIR A320 was at a height of 37,000ft, and disappeared after entering the Egyptian airspace with 10 miles"
"EGYPTAIR has contacted the concerned authorities and bodies and inspection is underway through the rescue teams."
The plane left Paris Charles de Gaulle at 2309 local time Wednesday (2109 GMT / 2209 BST /0709 Thursday AEST).
The BBC is also reporting Greek Defence Minister Panos Kammenos as saying that the flight "fell 22,000 feet, spun sharply before disappearance".
The Egyptair website had earlier been down, but now redirects to an "emergency" page with the following statement:
"EGYPTAIR denies all misleading information published by news websites and on the social media channels regarding the reasons of the disappearance of EGYPTAIR flight MS804 and the company confirms that the reason of disappearance hasn't been yet confirmed.
"EGYPTAIR Calls for media resources to be assured of the information they post or release and to abide by the official press releases issued by EGYPTAIR media center."