*UPDATE*
Egyptian officials say there are no survivors.
Egypt's prime minister has confirmed a passenger plane has crashed in Sinai.
The Airbus - with more than 200 people on board - disappeared off radar after leaving Sharm el-Sheikh. The jet was travelling to St Petersburg, and is thought to be from the Russian airline Kogalymavia - which also trades as Metrojet.
There was confusion about the plane earlier, with reports saying it had been spotted over Turkey.
The wreckage has been spotted, and over 40 ambulances are attending the scene. It's understood the plane split into two parts.
Most of the people on board are thought to be Russian, and Russian President Vladimir Putin has ordered Russian rescue teams to the crash site.
However - former air crash inspector Tony Cable says they won't be in control of the investigation:
Sky's Russia correspondent John Sparks says the pilot asked Ground Control to change route:
Relatives of those on board have begun arriving at Pulkovo Airport in St Petersburg, where they're being directed to a crisis centre.
