A large power cut hit more than 2,200 homes across several areas of Norfolk and beyond on Wednesday.
UK Power Networks said they were first made aware of the issue at 8.37am.
By 8.56am the utility firm said it had restored power to more than half of the affected homes and businesses remotely, leaving 1,023 without electricity.
Engineers have been sent out to investigate a suspected issue affecting an underground cable.
Some affected areas in Norfolk and Waveney include Attleborough, North Walsham, Winterton-on-Sea, Gorleston-on-Sea and Carlton Colville, near Lowestoft.
The same problem has also hit some people living in parts of Cambridgeshire, Hertfordshire and Essex.
Not all homes in these areas will be affected, but those hit may be without power for several hours.
UK Power Networks hoped to resolve the issue by 11am, and by that point had restored power to most of the homes.
However, "a lot of work is required on site" to fully resolve the issue, meaning the estimates completion time has been pushed back to 3pm.
The firm is providing temporary generators for those who are still without power to provide them with electricity while engineers go about their work.
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