Shetland Coastguard has been tasked to help an offshore worker who has fallen ill on a platform 77 miles east of the island.
The helicopter took off at 9.50am, and is currently on its way to collect the worker.
It is anticipated that they will land back in Shetland for hospital treatment at around 11.15am.
A coastguard spokesman said: “The coastguard search and rescue helicopter is en route to an offshore installation to evacuate an ill crewperson.
“The installation is 77 miles to the east of Sumburgh.
“We were told initially at 9.23am, and the helicopter left at 9.50am.
“They are still on their way out there, and are aiming to get back to a landing site on Shetland for hospital treatment at about 11.15am.”