In the South Island Dunedin Airport was -4.8C, Queenstown was reporting -3.4C and Christchurch, also frosty at -2.2C at 7am.
The central South Island recorded the coldest temperature in the Mackenzie District in South Canterbury with -7.2C overnight.
In the North Island, things were a bit warmer with Kiwis waking up to 5.7C in Auckland and 6.3C in Wellington.
Tomorrow is a different story, with a "complex trough" moving across New Zealand, bringing rain and clouds.
"If you happen to be working through the weekend and have Monday and Tuesday off, you're going to be in a very unfortunate situation," Adams said.
The slow-moving system will cause heavy rains to linger in most of the main centres, although Christchurch may catch some clear skies.
"The effect of this trough will be felt across the country through into the following weekend, basically."
The "fairly mature" system had come across from the tropics, and there had been enough time for the air to get "fairly well mixed", so temperatures would not be particularly cold, but neither would they be particularly warm.
There should not be strong winds initially, although there will be "decent amounts of rain" through the week.
MetService has put out a severe weather outlook to warn of a risk of heavy rain from Monday to Tuesday throughout the central North Island and from Taranaki to the Bay of Plenty.
There could also be heavy rain around the west coast of the South Island, as well as Buller and Nelson.
"It's just going to feel a bit miserable, to be honest," Adams said.
On the bright side, the ski fields should be high enough to receive good top-ups on snow, he said.
