Mechanical failure may have caused a helicopter crash in the North Sea, which killed five people and left another six feared dead.

Two Teesside workers are feared to be among the victims of the disaster.

Five bodies and some wreckage were recovered within two hours of the tragedy, which happened when a Sikorsky S-76 helicopter went down some 30 miles off the Norfolk coast on Tuesday night.

The Air Accidents Investigation Branch has launched an inquiry but rescue teams and experts said initial indications were that the aircraft, operated by Bristow Helicopters, suffered "major mechanical failure".

Helicopter accidents in the North Sea usually occur in bad weather yet conditions at the time were said to be good with visibility of up to five miles.

Sea King pilot Flight Lieutenant Paul Hopson, who was scrambled to the scene from Suffolk, said: "There was no Mayday call and certainly no emergency beacons were activated, which suggests it happened very quickly."

Coastguards reported that the aircraft appeared to "spiral down" and hit the water soon after taking off from the Shell/Esso-operated Clipper platform for the Global Santa Fe Monarch drilling rig nearby.

The pilot may even have attempted to put down on the platform but fell "tragically short".

Two pilots from Bristow, three Shell staff, three staff from engineering firm AMEC - which has bases in Wallsend, Darlington, and Sedgefield - two AMEC sub-contractors and one person from Oilfield Medical Services were on board.

Northern Constabulary in Scotland, named one of the missing passengers as Angus MacArthur, 38, of Birch Drive, Maryburgh, Ross-shire.

The Queen, who flew to East Anglia yesterday using a Sikorsky S-76 similar to the one that crashed, sent a message of condolence to relatives.