Eleven of those on board were Norwegian, one was British and one Italian.Photos from the scene show thick smoke coming from an area of rocky islets.
Meanwhile Norway's civil aviation authority has imposed a flight ban on the type of helicopter that crashed - the Eurocopter (EC) 225L Super Puma.
The helicopter was "totally destroyed", reports said. It was flying from the Gullfaks oil field to Bergen, a centre for the North Sea oil and gas industry.
Oil company Statoil said the aircraft was "on assignment" for it.
It came down near the small island of Turoey, just west of the village of Solsvik.
Police spokesman Morten Kronen said a major operation, which included firefighters, divers and medical workers, was under way to find the two missing people.
