A search and rescue operation was under way on Thursday after an EgyptAir Airbus A320 with 66 people on board vanished from radar en route from Paris to Cairo, the airline said.
A tweet on the airline's official account said flight MS804 left Paris at 11:09 pm local time, "heading to Cairo (and) has disappeared from radar".
Further tweets in Arabic said contact was lost at 2:45 am Cairo time, when the plane was just inside Egyptian airspace and at an altitude of 37,000 feet (11,000 metres).
The airline said in a statement that Egyptian military search and rescue teams were combing the area where the jet might have gone down.
There were 56 passengers, seven crew members and three security men on board, the statement said, adding the passengers included a boy and two babies.
Ahmed Abdel, the vice-chairman of EgyptAir holding company, told CNN that search and rescue teams were now at the scene.
"Daylight has just broken around an hour ago, so we should get some information within the next hour," he told the channel.
There were no distress calls from the plane, he added.
The flight from Paris Charles de Gaulle airport to Cairo normally takes just over four hours and the plane was due to arrive at 3:05 am local time.
EgyptAir said the plane had been manufactured in 2003.
EgyptAir hit the headlines in March when a flight from Alexandria to Cairo was hijacked and forced to divert to Cyprus, where the "unstable" hijacker demanded to see his ex-wife.
In October, the Islamic State group claimed responsibility for bombing a Russian airliner carrying holidaymakers from the Egyptian resort of Sharm El-Sheikh, killing all 224 people on board.
The disappearance of the jet on Thursday comes more than two years after the start of one of the most enduring mysteries in aviation history.
Malaysia Airlines Flight MH370 vanished on March 8, 2014 en route from Kuala Lumpur to Beijing with 239 passengers and crew on board, mostly Chinese and Malaysians.
Authorities believe the Boeing 777 detoured to the remote southern Indian Ocean and then plunged into the water.