A "major incident" has been declared on Shetland after a damaged underseas cable led to all communication lines being shut down.
Engineers are working to fix the complete outage on the remote island in the North Sea.
Phones, internet and computers are not usable, leaving the island cut off from the mainland, Shetland police said.
Local officers were patrolling to try to reassure residents, added the statement from Police Scotland.
There have also been reports that many shops are unable to take card payment due to the ongoing incident.
Scottish First Minister Nicola Sturgeon said the incident was an emergency situation for the island.
She added it is assumed that the damage was accidental, as she explained: "There is nothing to suggest otherwise, but work is continuing to assess exactly what the cause of the problem has been."
Alastair Carmichael, MP for Orkney and Shetlands, said he raised the issue with the UK government, but it could take days for communications to be restored.
In a statement, Shetland police said: "Engineers are working to fix a complete outage on Shetland affecting its connection to the main line.
"Phones, internet and computers are not usable.
"Officers will continue to patrol the area and we will give you an update on the situation as soon as we have more information."
BT Group said a south subsea cable between the islands and mainland had been cut.
A spokesperson told the BBC: "Due to a break in a third-party subsea cable connecting Shetland with the Scottish mainland, some phone, broadband and mobile services are affected.
"Engineers are working to divert services via other routes as soon as possible and we'll provide further updates. Our external subsea provider is also looking to restore their link quickly.
"Anyone who needs to call 999 should try their landline or their mobile, even if they don't have signal from their own mobile provider. We're sorry for any inconvenience."
Officers are continuing to carry out patrols and residents have been told not to make non-urgent calls and check on elderly and vulnerable people more frequently.
Superintendent David Ross said: “We are advising people not to make non-urgent calls for the time being so that all available lines can be used for emergencies if required.
“In an emergency the public should try calling 999 on their landline or mobile.
"If that does not work you should go to your nearest police station, ambulance station, fire station or hospital to report an emergency or try flagging down an emergency services vehicle that does not have its blue lights on.
“Officers are patrolling in vehicles and on foot and we are working with partners to make additional resources available.
"I would ask that relatives and neighbours of elderly or vulnerable people check on them regularly. Assistance alarms may not be operating correctly.”
The isles are located 130miles from the Scottish mainland and have a population of about 23,000.
The incident comes amid heightened interest over the suspected "sabotage" of the Nord Stream pipelines - which bring Russian gas to Germany - last month.
The underwater pipeline is thought to have been destroyed by a blast, after "powerful explosions" left four holes in the pipe, said Danish police.
It is still unclear exactly what caused damage to the underseas cable connecting Shetland to the mainland, said police.
However, it comes as repairs are being made to another cable linking the Shetland and Faroe islands, after it was damaged last week.
