Photo: RNZ / Russell Palmer
Households are being warned that unless they conserve electricity, they could face possible power cuts on Friday.
The national grid operator Transpower said there could be insufficient supply between 7am and 9am, because of an unseasonal cold snap and low wind generation.
"Transpower will work with electricity lines companies around New Zealand to switch off controllable load like hot water systems tomorrow morning to reduce demand," it said.
"Hot water systems are regularly switched on and off during the day, so most people won't notice this."
It said if action from lines companies, major industrial consumers and households did not conserve enough electricity, it might not be enough to keep the lights on everywhere.
"Transpower may need to work with lines companies to switch off supply to some areas around New Zealand," it said.
"This would be for a short time until the electricity supply shortage is resolved and will prevent the risk of widespread and longer outages."
Transpower said households could help by turning off heaters and lights in unused rooms, delaying using appliances, and not charging devices and cars.
"It is forecast to be a very cold morning, and people should stay warm by heating rooms they are using and continuing to keep them warm. However, they could consider turning down the temperature slightly between 7am-9am," it said.
Transpower issued a warning notice to the industry earlier on Thursday.
Transpower chief executive general manager Chantelle Bramley told Checkpoint generators were doing scheduled maintenance before winter.
Bramley said the whole industry was coming together to avoid power cuts.
"This time of year can be challenging, generators are taking necessary scheduled outages to do maintenance on their power plants prior to winter, they have to do maintenance on these plants."
It was unseasonably cold weather, she said.
"We will work with lines companies to, as a last resort, switch off power to locations for a short period of time."
Asked if she could guarantee this wouldn't happen during the colder months, Bramley said no.
"No power system can absolutely guarantee supply but as we've seen today, when industry comes together we can make sure there is enough in the system."
MetService has forecast temperatures to plunge overnight, with Christchurch set to fall to -4 degrees Celsius.
In 2021, almost 34,000 households lost power on one of the coldest nights of the year, as insufficient supplies were arranged for the surge in demand.
An industry panel fined Transpower $150,000 for its role in the blackouts.