The national grid operator Transpower has issued a New Zealand-wide emergency over power shortage.

Its system operator advises there is a risk of insufficient generation and reserve offers to meet demand and provide coverage in a major N-1 event, which would be an event such as one of the five turbines at the Huntly Power Station failing unexpectedly.

Transpower asks people to reduce their power consumption if possible, by turning off non-essential lights and delaying charging mobile and laptop devices.

Normal generation is due to resume about 9am, and Transpower is working with local lines companies to manage controllable load by turning off hot water systems, says the spokesperson.

It warns that if the response from power companies was insufficient it might need to 'manage demand” by disconnecting power supplies 'without further notice”, which would mean a repeat of the power cuts that occurred on August 9 last year, when power was cut to 34,000 homes, reports Stuff.

Transpower warned in May that there was a heightened risk of power cuts on 37 days between June and August, singling out July 26 as a day for another potential grid emergency, but said then that it expected the risks to decrease as the dates got nearer and power companies responded to its warnings.

Transpower spokesperson Nathan Green says shortly before 9am that the shortage today had been caused by an issue at the Stratford 'TCC” gas power plant, which is owned by Contact Energy, and a sudden drop in wind speeds.

It expects it would be able to get through the 'morning peak” thanks to power companies managing ripple-controlled water unless anything unexpected happened, he says.

-RNZ.