Energy Minister Gerry Brownlee has described the failure of one of two Cook Strait power cables on Monday night as alarming.
Transpower is working to repair the cable, which went out apparently because of a transformer failure. The work could take up to a week to complete.
Mr Brownlee says emergency power can still be delivered from the South Island to the North Island by the second cable, known as Pole 1, which is 43 years old and due for replacement.
He says there should not be any power cuts because there is sufficient generation capacity in the North Island, but he says it could have been a different story if it had been the middle of winter.
Mr Brownlee says there are no immediate implications for consumers because there is enough generation capacity in both islands.