The country has narrowly avoided the need for power cuts as households and big industrial users rallied to conserve power on an unseasonably cold morning.

National grid operator Transpower warned on Thursday that there could be insufficient supply between 7am and 9am on Friday.

It asked people to reduce their use of power by turning off heaters and lights in unused rooms, delaying using appliances, and not charging devices and cars.

The Major Electricity Users' Group (MEUG), which represents big industry, said the sector had freed up about 60 megawatts of power in response.

While those savings would hit production in the short-term, the group's chair John Harbord said that was what they signed up for as responsible New Zealanders.

Despite overnight temperatures dropping well below zero in some areas of the country, New Zealand had managed to save over 260MW, Transpower's executive general manager, Chantelle Bramley, told RNZ's Morning Report.

That represented "a very significant response", she said.

"As you know, the situation was very tight; we've had really cold weather. We just want to thank New Zealanders for their fantastic response this morning, it has made a huge difference getting us through the morning peak."

Bramley said Transpower had been prepared to work with lines companies to control the load if necessary, but "thankfully we didn't get to that situation, we didn't have to call for any further load management".

"The networks were working really hard to manage load ... and we've avoided any further need to switch off supply."

Harbord told Morning Report MEUG had two concerns: One was that there was not a strong argument for spending millions of dollars on a new plant if it sat unused apart from times of big demand.

The other was the mix of electricity generation; as there was more reliance on renewables, such as solar and wind, situations such as Friday's could arise more often, he said.

"A bit more thermal peaking would be really helpful, because the thermal sits there, you can stockpile gas and coal and turn it on almost in an instant and the problem we have with solar and wind, you can't stockpile it and save it for when you need it."

'This is not where we want consumers to be'

Energy Minister Simeon Brown told Morning Report his expectation was that generators and regulators (Transpower and the Electricity Authority) would have had security of supply as a top priority going into winter.

"We've had a number of winters where there has been tightness in recent years and there has been changes made around how information is shared, how decisions are made, how warnings are provided to ensure that the market and the system operates as best possible for consumers.

"But ultimately, this is not where we want consumers to be with these types of warnings. We ultimately want a secure, reliable electricity system where Kiwis are able to stay warm and the light in winter time."

Transpower has said the problem with supply was due to 700MW of generation being offline due to maintenance.

But Brown said "part of the reason" for the squeeze was that New Zealand had "old thermal generators, which means when we have to turn it on, some of it's not always available".

He also blamed on the previous government's ban on new gas exploration, the "frankly impossible" 2030 100 percent renewable target and the Lake Onslow battery scheme, which he said had a "chilling effect" on new investment from the market.

The Labour Party's energy spokesperson, Megan Woods rejected that, telling Morning Report the country needed ways to store electricity.

The Lake Onslow battery scheme would have done that, she said, but the coalition government had ditched it and had no plans for other storage options.

Suppy expected to hold up over coming days

Transpower's Bramley said the grid operator was not concerned about any further supply issues at this stage.

"We're expecting pressure to drop off later this afternoon; we're not looking at any potential issues over the coming days."

The 700MW that were currently offline due to maintenance were due to come back online over the next few weeks, she said.

May was always a challenging month with lots of outages, Bramley acknowledged, but she said generators had done an amazing job ensuring there was as much supply as possible available on Friday morning.

She said the timing of future maintenance would be looked at but said investment in the system was also necessary to make sure there were enough flexible resources to be able to respond to unseasonably cold days.

Main image (RNZ/Jean Edwards): A frosty fencepost in rural Canterbury.