An EgyptAir jet sent a burst of error messages indicating that smoke had been detected on board before crashing into the Mediterranean on Thursday, France's BEA air accident investigation agency said on Saturday, confirming media reports.

"These messages do not allow in any way to say what may have caused smoke or fire on board the aircraft," a spokesman for the agency said, adding that the messages indicated that smoke been detected towards the front of the cabin.

He said the priority now was to find the aircraft and its two flight recorders containing cockpit voice recordings and data readings. The Airbus A320 vanished from radar on its way to Cairo from Paris with 66 people on board.

The flight data was sent through an automatic system called the Aircraft Communications Addressing and Reporting System (ACARS), which routinely downloads maintenance and fault data to the airline operating the aircraft.

Aviation website Aviation Herald published a burst of seven messages broadcast over the space of three minutes. These included alarms about smoke in the lavatory as well as the aircraft's avionics area, which sits under the cockpit.

While suggesting a possible fire, the relatively short sequence of data gives no insight into pilot efforts to control the aircraft, nor does it show whether it fell in one piece or disintegrated in mid-air, two aviation safety experts said.

The BEA is assisting an official investigation into the crash, which has been launched by Egypt's air crash investigation authority.