A helicopter believed to be carrying 18 passengers has ditched into the sea west of the Shetland Isles, Sky sources have said.
A ferry travelling from Shetland to Orkney is understood to have been asked to turn round and help.
The incident happened two miles west of Sumburgh airport, which is at the very southern tip of the main island.
It has been reported that the helicopter is operated by CHC, taking people to and from oil and gas platforms in the North Sea.
Sky News has been told it was a Eurocopter Super Puma AS332 L2, a model that normal has a good safety record.
RNLI lifeboats are also believed to have been launched to help in any possible rescue mission.
The ferry which has been asked to turn round left Lerwick at 5.30pm.
It is not known if there are any casualties.