Egyptian President Abdel Fattah al-Sisi said on Sunday no theory was being favoured on why EgyptAir MS804 plunged into the Mediterranean, after sending out an automated message signalling smoke onboard.

The Airbus A320 carrying 66 people had crashed into the sea while flying from Paris to Cairo early Thursday, and some wreckage but not the black boxes has been found.

Egypt's aviation minister had said that terrorism was more likely than technical failure, but Sisi said in a televised address that "all the theories are possible".

"There is no particular theory we can affirm right now," he said.

READ: EgyptAir MS804: Egyptian army post images of plane debris

READ: 'Smoke on board' EgyptAir plane before crash

A civil aviation official told AFP on Sunday that search teams had found none of the passengers' bodies, as the search continues.