A helicopter with 12 passengers and two crew has crashed in the Baltic Sea about three miles from the Estonian capital, Tallinn.

The Sikorsky 76 was on a scheduled flight from Tallinn to Helsinki, Finland, says the Estonian rescue service.

The aircraft's tail section was sticking out of the water when rescuers arrived, but the rest of the aircraft was submerged, said Mati Raidma, head of the rescue service.

"The rescue mission is going on," he said.

The cause of the crash was not immediately known. A storm in the area caused operators to cancel the fast ferries between Tallinn and Helsinki.

Finnish news agency STT, citing Estonian Embassy officials in Helsinki said the passengers were six Finns, four Estonians and two US citizens.

Later eyewitness reports suggested the entire helicopter had sunk and rescuers found only scattered wreckage on the surface.

"We couldn't find anybody, only debris," said Estonian maritime rescue service spokesman Aivar Muriks, adding that divers were searching for survivors.