The Danish Baltic Sea island of Bornholm experienced a complete blackout Monday morning.
Electricity operator Energinet said an underwater cable that provides electricity from Sweden is now back online after it went out at around 8 am.
The island is located between Sweden and Germany and is close to where the recent Nord Stream gas leaks were discovered.
Both the West and Russia blamed each other for the damage to the pipelines.
Since then, Denmark has increased security around its energy infrastructure.
Bornholm is an important naval base and home to nearly 40,000 people.