All 13 people aboard a helicopter that crashed off the coast of Norway Friday are believed to be dead, as local media report the rotor blades flew off before the aircraft went down.

The helicopter had departed from an offshore oil platform. The wreckage of the rotor was found at least 600 feet from the rest of the aircraft, Norwegian broadcaster NRK reported.

At the same time, the Norwegian Civil Aviation Authority said it immediately was banning helicopters of the same type as the one that crashed -- Airbus Helicopters EC225LP -- from flying over Norway or near its offshore facilities.

The Norwegian newspaper VG reported all 13 people on the helicopter were believed to have died. It also reported that scheduled maintenance on the helicopter was delayed twice last year.

Eyewitness Rebecca Andersen told the newspaper that the helicopter's "rotor blades came rushing toward us... Then we heard a violent explosion."

Police spokesman Morten Kronen told The Associated Press that the helicopter "has crashed, it is totally smashed."

Kronen added there were "reports of an explosion and thick smoke" and that there were people in the sea just west of Bergen, Norway’s second largest city.

On board were 11 Norwegian nationals, one Briton and one Italian, according to Jon Sjursoe, a spokesman for Norway's Joint Rescue Coordination Center.

The area sees frequent helicopter traffic as passengers are shuttled to and from oil platforms. The helicopter that crashed was making a 74-mile journey from the Gullfaks B oil platform, operated by Statoil, to Bergen.

Statoil said in a brief statement it had "mobilized its emergency response team" but declined to immediately comment further.

Norwegian media posted photos of huge billows of smoke. In one image broadcast on Norwegian television, pieces of red debris could be seen on a rocky outcrop along the island.

Norwegian Prime Minister Erna Solberg wrote on Twitter about the "horrifying reports" and said she was being kept informed about the rescue work.

The Associated Press contributed to this report.