The Airbus A-321 had just left the Red Sea resort of Sharm el-Sheikh, bound for the Russian city of St Petersburg. Wreckage of the plane has been found in the Hassana area. It disappeared from radar screens when travelling at 9,500m (31,000ft), Egyptian officials said.
Egyptian officials said most on board are likely to have died. The plane was operated by the small Russian airline Kogalymavia, based in western Siberia.
Russian authorities say it was carrying 217 passengers, 17 of them children, and seven crew. Most were Russian tourists. it is likely there will be speculation about militant involvement in the incident - Sinai has an active millitant network, with local Jihadis who have allied themselves to so-called Islamic State.