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The wintry temperatures are set to continue into the weekend, with another unusually cold night expected on Thursday, MetService says.
Households were warned that unless they conserved electricity, they could face possible power cuts on Friday.
MetService meteorologist Ngaire Wotherspoon said "The current cold spell isn't going anywhere, and tonight (Thursday) will likely be the coldest of the lot."
Her colleague, meteorologist, John Law said where there were clear skies, temperatures were expected to drop.
"Another very cold night, frosty conditions, perhaps even some severe frosts through some of those inland parts of Canterbury and across some of those more inland parts of the central North Island."
In the early hours of Friday morning, central parts of Auckland will see temperatures down to 3 degrees, with temperatures below freezing for parts of Waikato, Central High Country and towards parts of Manawatū and Wairarapa.
Auckland can expect a high of 14 degrees on Friday, 13 degrees in Wellington and Tauranga should see a high of 15 degrees before another cold night heading into Saturday.
Christchurch can expect -4 degrees and a cold and frosty morning on Friday.
Towards the end of Friday showers were forecast for the far northern parts of the South Island.
"Plenty of clear skies are in store for the end of the week. For Friday, showers are forecast for southern and eastern areas as a weak front moves north, but we are expecting widespread dry weather for the weekend," Wotherspoon said.
Relief from the chilly conditions was on the horizon, as southerly winds eased over the weekend, but the remaining cold air was forecast to stick around into next week, according to MetService.
"These cold nights are set to a continue for a while, but warmer, wetter weather should return later in the week," Wotherspoon said.
The weekend
MetService said Saturday would see showers in the east of the North Island easing, and a few early showers about Wellington and Taranaki, while fine elsewhere on the motu.
For the South Island, showers were expected in the far South as well as some morning showers about Canterbury and Marlborough, but fine elsewhere.
Sunday was forecast to be mainly fine for most. However, isolated showers were predicted in the west from Taranaki to Wellington, and for Buller, northern Westland, and the far south.