Egypt's civilian aviation ministry said the plane had been at an altitude of 9,500m (31,000ft) when it disappeared.
Live flight tracking service Flight Radar 24's Mikail Robertson confirmed the altitude.
He told the BBC that the plane started to drop very fast, losing 1,500m in one minute before coverage was lost.
Unconfirmed reports are that the pilot declared an emergency due to a ‘technical fault’ and requested to be diverted to Al-Arish airport in Sinai.