In West Auckland the weather station at Whenuapai was registering -3C at 5am and at Ardmore, in east Auckland, the mercury was sitting at 0C.
Bellam said even the winterless north would wake to frosts with main centres Kaitaia on 2C and Whangarei on 2.7C.
Niwa recorded the four coldest North Island locations as Hamilton and Matamata sharing a bone-chilling -2.1C, Rotorua slightly warmer on -2C and Warkworth on -.9C.
The coldest temperatures for the country were reserved for the South Island, where St Arnaud in Nelson Lakes National Park recorded -4.9C and Twizel -4.2C.
Bellam said the polar blast had by and large cleared the country, with just a few snow flurries on the Remutaka Hill Rd and in the Gisborne region overnight.
However, a few showers would cross the eastern coastlines of both islands across the day.
"We're still just getting some residual showers around in the south and east of the South Island and skimming up the east coast of the North Island with a little surge of showers coming back into Wellington this evening, but basically most of that has moved offshore."
He warned that giant swells would be pulsing up from Wairarapa through to Gisborne during the day.
Southern and eastern coastal parts of Wellington remained under a local state of emergency and a heavy swell warning remained in force for Wellington until 11pm.
The Desert Rd and SH87 in Otago remained closed this morning because of snow and ice.
