Temperatures plummeted to well below zero overnight in many parts of the country.
The Canterbury high country recorded the coldest temperatures, with Mount Cook falling to -13.3°C and Tekapo dropping to about -10°C.
Christchurch reached a low of -6°C, and in the Southern Lakes it was -8°C.
In the centre of the North Island, the Desert Road and Waiurou got down to about -7°C.
A Metservice duty forecaster, Kyle Lee, said some areas would have had severe frosts.
"We got down to quite a lot of negatives in a lot of areas due to the clear skies for most of the country."
Meanwhile, Auckland had its coldest night for two years - at 1.4°C.
How cold was your region last night? Sub-zero temps up and down NZ last night, Mount Cook in Canterbury High Country wins with -13.3C. ^TA pic.twitter.com/HmaNoKAX6w— MetService (@MetService) July 29, 2017