A nationwide request for power providers to reduce load on the national grid saw thousands of homes across Hawke's Bay without power for parts of Monday evening.
A spokesperson for Transpower, which manages the national grid, said demand for electricity across the country was at an all-time high.
Insufficient generation meant it was unable to meet demand and manage a secure system.
"As a result, Transpower has asked the distribution companies to reduce load," she explained.
"Different companies will do this in different ways, some manage via load control on hot water, some manage via customer disconnections."
She said the situation was expected to resolve at 8:00pm on Monday once peak demand for electricity had passed.
Close to 10,000 homes across Napier, Rotorua and Taupō reported power outages shortly before 7pm.
Most of these homes had their power restored before 9pm.
Unison spokesperson Danny Gough confirmed it was not a network fault and part of a nationwide request for electricity lines companies to reduce their load by about one per cent.
He said this was to ensure the integrity of the main grid could still be maintained.
Unison was doing this by conducting a series of rolling power outages across Hawke's Bay, Rotorua and Taupō.
"We're changing this out all the time to minimise the impact.
"It's really inconvenient and we obviously realise the frustration that some people are feeling because of that.
"We sincerely apologise that we were unable to provide you with information about these outages earlier, but this was a very dynamic and quickly evolving situation.
"We appreciate your understanding and support."
Gough said the increased demand had likely been driven by the cold snap hitting much of the country.