French prime minister Manuel Valls said no scenario could be ruled out at the moment.

Aviation expert Rusty Aimer told Sky News EgyptAir and the Egyptian air traffic control facility are finding out whether there were any radar outages in the sector.

He said it could be one reason why they lost control of the aircraft.

"The other reason could be the aircraft itself disappearing, which could mean not a good ending," he said.

Air travel expert Julian Bray said no alert being made could mean the airliner suffered a "catastrophic failure" possibly as a result of an explosion.

"There's a lot of concentrated focus on terrorist issues around Paris but one has to be cautious about drawing conclusions.

"It would not have needed to be a large device - if it was a terrorist-related failure - to lose cabin pressure," he added.

European air traffic network manager Eurocontrol said there were no weather issues at the time of the plane losing contact.

Officials at France’s foreign ministry were looking into the matter but had no immediate information to report when contacted on the disappearance of the jet or on whether it could have been the result of a terrorist attack.

An EgyptAir flight from Alexandria to Cairo was hijacked in March 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.

Source: AFP