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Both the Queen and Tony Blair have offered condolences to relatives.

While the search, particularly for the flight data recorders, continues, Great Yarmouth coastguard said on Thursday morning no further progress had been made overnight.

Shell Chairman Clive Mather: "Tragic accident"

Mr Blair promised the investigation into the crash would "leave no stone unturned".

On Wednesday at 0720 BSTGreat Yarmouth coastguard scaled down its search and rescue operation for the other six passengers and crew.

Two vessels equipped with sonar are still searching the area, trying to find wreckage on the sea bed.

A diving support vessel from Aberdeen, the Mayo, is making its way to the crash site.

It will help salvage the wreckage - and any bodies inside - once the helicopter has been found.

Speaking in the House of Commons, Mr Blair paid tribute to the efforts of the emergency services, saying they had responded "as they always do, in magnificent fashion".

Four inspectors from the Air Accidents Investigation Branch (AAIB) are at the crash scene carrying out an inquiry.

Flight Lieutenant Paul Hopson of the RAF search team said: "All the indications are of a major mechanical failure."

Co-pilot Flight Lieutenant Steve Murkin said: "It looked like it must have been something quite catastrophic.

"It was not a controlled ditching as we had hoped."

Routine trip

John Balls, of Cromer lifeboat, told the BBC that some time may have been lost due to initial confusion over the number of people in the helicopter.

"We just got a position and we were on our way.

Police forensic officers return from the scene

"Then we were recalled a couple of minutes later because they said they had picked up four persons out of the water.

"But when we were rehousing they then called us back because obviously there was a muddle as there were 11 on board."

Clive Mather, chairman of Shell UK, which chartered the helicopter, described it as a "terrible accident".

The helicopter was on a routine trip from Norwich Airport to North Sea rigs.

It left Norwich at 1900 BST on Tuesday with nine workers and two crewd, flew to the Clipper gas platform in the North Sea, and then continued to the Santa Fe Monarch gas drilling rig.

It was on this leg of the journey that the helicopter crashed, two miles from the rig and 25 miles north-east of Great Yarmouth.

Sea King scrambled

Keith Chanter, chief executive of Bristow, which operated the aircraft, said: "As it approached the rig, the aircraft inexplicably ditched in the sea."

An RAF Sea King from Wattisham in Suffolk was scrambled and five bodies were recovered from the water within two hours.

Mr Mather said the helicopters went through "rigorous maintenance schedules" and had a "very good" safety record.

The company has suspended all helicopter flights to and from the rigs in the southern North Sea.

Bristow said the helicopter was fully fitted with safety equipment including flotation bags to hold it afloat long enough for people to get out.

Survival suits

All the people on board would also have been wearing survival suits - standard practice for travelling to the rigs.

The two crew on board worked for Bristow, three of the passengers were Shell staff, three worked for engineering firm Amec and two for Amec subcontractors.

The remaining passenger was from Oil Field Medical Services.

Cleveland Police said two of the dead men were from the Teesside area.

Another eight of the people on board come from Norfolk and Suffolk.

None has yet been named.

Northern Constabulary in Scotland confirmed that one of those missing in the crash is Angus MacArthur, 38, from Maryburgh in Ross-shire.

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