An air and sea search is underway after a passenger was reported to have fallen overboard from a ferry.
The coastguard was alerted at around 5.30am to the person missing from the NorthLink ferry MV Hrossey in the Northern Isles.
A coastguard helicopter is involved in the search south-west of Fair Isle and three lifeboat crews are making their way to the scene.
The coastguard would not confirm the age or the gender of the missing person.
A review into offshore helicopter operations in the North Sea will compare UK fleets with those in Norway.
The CAA said its review will be undertaken with the Norwegian CAA and the European Aviation Safety Agency and will pay particular attention to:
- Operators' decision making and internal management
- The protection of passengers and crew
- Pilot training and performance
- Helicopter airworthiness.
The review follows five accidents in the last four years, the last of which in August this year claimed four lives.
The Civil Aviation Authority (CAA) has announced a review of offshore helicopter operations in the North Sea after an aircraft carrying 16 oil workers went down in August, killing four people.
The Helicopter Safety Steering Group temporarily grounded the Super Puma fleet after the incident, but lifted the ban after concluding that there was no evidence to support it.
The CAA said the review will be undertaken jointly with other safety watchdogs and advised by a panel of independent experts in order to make recommendations aimed at improving the safety of offshore flying.
There is no evidence of a technical failure on a Super Puma helicopter which crashed into the North Sea off Shetland killing four people that has been identified, according to air accident investigators.
Chancellor George Osborne will offer his condolences to relatives of the North Sea helicopter crash victims in a speech in Scotland next week.
Mr Osborne will use a trip to the north east oil and gas industry hub Aberdeen to pay tribute to "brave" offshore professionals who carry out their jobs in "an inherently dangerous environment".
Three men and one woman were killed when a Super Puma helicopter carrying workers from an offshore vessel crashed into the sea as it approached Shetland last Friday. Fourteen people survived, including two crew.
Unite Scottish Secretary Pat Rafferty insisted the Super Puma fleet of helicopters must remain grounded while workers' confidence remained "shattered":
A helicopter safety group has lifted its suspension on Super Puma commercial passenger flights to and from offshore oil and gas plants in the UK.
The Helicopter Safety Steering Group said the decision was based on confidence from a group of five unions and organisations after five days of safety reviews.
Les Linklater, Step Change in Safety's team leader, said: “We have had the opportunity to review key elements of our fleet and better understand the positions of the authorities that determine the airworthiness and operational compliance and safety of our helicopter fleet.
"The result is that there is no evidence to support a continuation of the temporary suspension of the entire Super Puma fleet."
The flight data recorder of a Super Puma helicopter that crashed into the North Sea, killing four offshore workers, has been recovered.
The helicopter plunged into the sea as it approached Sumburgh airport on the southern tip of Shetland on Friday, killing three men and one woman.
The search for the data recorder had been described as challenging due to the "nature of the environment" where the wreckage was located.
A statement from the Air Accidents Investigation Branch (AAIB) said: "The combined voice and flight data recorder from the AS332 L2 Super Puma helicopter has been successfully recovered and will be transported to the AAIB HQ in Farnborough later today."
CHC has temporarily suspended all flights of the three types of Super Puma helicopter that it operates - the L, L2 and EC225 following the fatal crash off the coast of Shetland.
Fellow operators Bond Offshore Helicopters and Bristow also enforced a temporary suspension of all Super Puma flights except emergency rescue missions, in the wake of a recommendation by the industry's Helicopter Safety Steering Group.
The freeze on using the helicopter type is causing disruption to the movement of workers both on and off shore.
Four oil workers were killed when a Super Puma AS332 L2 travelling from the Borgsten Dolphin support vessel came down off the southern tip of Shetland last week with 16 passengers and two crew on board.