A major sea and air search operation has been launched after a crew issued a distress call to say their boat was sinking.

Shetland Coastguard received the radio message from the vessel Still Water II at around noon.

The boat was thought to be off Scalloway Harbour on the west side of Shetland.

Coastguards, local boat users and harbour staff at Scalloway reported hearing a "frantic" message on the radio.

In an English accent the man identified his vessel as Still Water II, after which he said: “Calling Scalloway harbour, Scalloway harbour…all ships, all ships…coastguard, coastguard…I’m sinking, I’m sinking.”

Those who heard it said the message lasted less than 10 seconds before the line went completely dead. The coastguard attempted to re-establish contact the vessel but without success.

A coastguard spokeswoman said that lifeboats from Aith and Lerwick were dispatched, along with the Shetland coastguard helicopter.

The clarity of the signal suggested that the boat was close to Scalloway harbour. However a search of the entire area west of the harbour revealed no sign of any vessel in trouble.

Three coastguard rescue teams started an onshore search of the coastline from Weisdale south and around Scalloway but this was stood down at around 4pm.

The air and sea search will continue up to 10 miles west of Scalloway.