It is likely to be the end of the week before power is restored to all SSEN customers, the company has said.
SSEN engineers are battling “extremely challenging conditions” in their bid to restore power to almost 4,000 homes.
The company said the conditions were the worst engineers had faced in Shetland for 20 years.
Homes in Voe, Whalsay, Brae, Tumblin, Yell and Unst are still without power, with teams from SSEN out since first thing this morning.
Power has been successfully restored to over 2,500 properties, SSEN said.
The energy company said it expected to make progress today (Tuesday) in restoring power to customers in Yell and Unst, but continuing disruption means outages are likely to continue.
“Full restoration of customers is likely to extend to the end of this week,” SSEN said.
“This is particularly the case for outlying islands and localised faults and further information will be shared once all faults are assessed.
“We recognise the impact this may have on our customers and are working closely with local resilience partners to identify those who may need additional support and coordinate welfare arrangements.”
SSEN head of region Mark Macdonald said they had seen “extensive damage” to overhead power lines”.
“Our local teams have described the conditions as the worst they’ve seen in over 20 years.
“We’re moving engineers from the mainland to Shetland to assist with restoration efforts and have multiple teams ready to travel, pending improvements in the current travel situation.
“I’d like to reassure our customers we’re doing everything we can to restore power as quickly as possible and would encourage anyone who may be in a vulnerable situation to contact us on the power cut helpline, 105.”
A further update will be provided at 5.30pm today.