The Health and Safety Executive has joined police to investigate the death of a 49 year-old diver in the northern North Sea Sector.
The Shetland coastguard rescue helicopter was scrambled in an attempt to save the man who took ill while diving with the diving support vessel Acergy Osprey.
But by the time the helicopter made the 110-mile journey from Sumburgh to the Acergy Osprey which was off Unst, the man had been declared dead.
Initial reports suggest he may have suffered a heart attack.
A spokesperson for Aberdeen based Subsea7 who operate the Acergy Osprey said their immediate priority was to provide support to his family and colleagues.
The spokesperson added that an investigation is underway and the company is co-operating with the relevant authorities.
A spokesman for Shetland Coastguard said their helicopter planned to take the man to hospital in Lerwick, but he died before they could reach him.
The Acergy Osprey returned to Peterhead Harbour and the helicopter returned to its base.
Police said that the death was being treated as ‘unexplained’ and a report would be submitted to the procurator fiscal.
The Health and Safety Executive said that they were working alongside the police who are leading the investigation into the man’s death on Sunday afternoon.