Parts of the country are waking to below freezing temperatures, amid fears there won't be enough electricity to go around this morning.
Transpower has warned the crunch time for demand will be between 7am and 9am and there could be power cuts if demand is too high.
The coldest place is Christchurch on -6 , MetService said.
It's -2 in Masterton, Blenheim and Wanaka and zero degrees in Hamilton.
The warmest places are Invercargill and Dunedin on a balmy 10 degrees.
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MetService meteorologist John Law spoke to Morning Report from the Wellington waterfront.
"It's an unusually cold start to May, looking at some places like Christchurch, for example, down to minus 6.3 Celsius last night. That's unsually cold for any night in May ...that air coming up from the south.
"Then of course there's these nice clear skies we've had in the last few nights allowing any of that daytime heat to dissipate once the sun sets."
Part of the pressure on the country's power supply is due to the lack of wind for the wind farms.
Law said this was due to a big area of high pressure across the country so there were very as a very light winds across most of the country.
While the conditions could be attributed to a southerly polar blast, there would be no storms with a high pressure system keeping conditions clear.
He forecast more chilly nights to come through the weekend while next week would be warmer and wetter.
However, it would not be a boon for the country's skifields with no snow expected as part of the cold snap.
The sun is due to be shining in most places this morning, with a few showers scattered across the east coast.
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