There were conflicting reports about the fate of the plane, some suggesting it had disappeared over Cyprus.
Most of the passengers are said to be Russian tourists.
The plane was operated by the small Russian airline Kogalymavia, based in western Siberia. Latest reports say it was carrying 217 passengers and seven crew.
A “Russian civilian plane… crashed in the central Sinai”, the office of Egyptian Prime Minister Sharif Ismail said in a statement.
It added that Mr Ismail had formed a crisis committee to deal with the crash.
The Russian aviation authority Rosaviatsiya said in a statement that flight 7K 9268 left Sharm el-Sheikh at 06:51 Moscow time (03:51 GMT) and had been due into St Petersburg’s Pulkovo airport at 12:10.
The authority added that the aircraft failed to make scheduled contact with Cyprus air traffic control 23 minutes after take-off and disappeared from the radar.
A centre to help relatives of the passengers has been set up at Pulkovo airport, Tass news agency quoted St Peterburg city officials as saying.