The SIC are closing the B9073 road, known as the Black Gaet, due to wintry weather on Tuesday evening.
The council said continued build-up of lying snow on the road is making driving hazardous and a decision has been taken to close the road to all traffic with immediate effect.
Council staff are currently placing signs at the two junctions with the A970, at the west junction, nearest Scalloway; and at the east junction, nearest Gulberwick and Lerwick.
The road will reopen when weather conditions improve and the road can be cleared of any accumulated snow, the SIC said.
An alternative route exists via Lerwick.
Almost all of the council’s bus services have also been cancelled.