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Pukaki Airport - near Twizel in the South Island's Mackenzie District - was the country's coldest spot, dropping to a freezing -7C, MetService meteorologist Bill Singh said.
Dunedin Airport was a very chilly -4C, while the city centre was on 2C just before 7am. Christchurch residents were shivering through a low of -3.4C.
Central Otago experienced a hard frost and reported temperatures as low as -6degC.
The Central Otago District Council, in a Facebook post, are cautioning motorists as ice has been spotted on bridge decks and shaded areas.
Crews gritted the areas and have been patrolling the roads this morning,
The Danseys Pass Rd remains restricted to 4WD vehicles.
Further north, Auckland dipped to 5C, it's equal coldest morning this year along with June 3.
Wellington by comparison was a balmy 9C overnight.
Singh said the major issues brought by the big freeze were frosts after only the North Island's east and Wairarapa coasts had rain overnight.
Fellow forecaster WeatherWatch said a large high rolling in from the Tasman Sea was locking cold air over the country.
"A southerly change followed by a large high is often the perfect recipe for cold nights and that's precisely what is happening," the forecaster said.
The consolation for Kiwis is that sunny skies will blanket most of the country today.
Auckland is set for a fine morning and top of 14C before dropping to an overnight low tonight of 8C.
Temperatures then warm to 16C and 17C on Thursday and Friday, but persistent rain is forecast for most of the North Island from tomorrow.
Whangārei residents can expect a top of 16C today with tonight's forecast low of 12C about 5C higher than last nights low of 7C.
Hamilton and Tauranga can expect sunny tops of 13C today. The chilly frosts will continue in Hamilton where another overnight low of 1C tipped tonight before rain hits from tomorrow.
New Plymouth and Napier are both expecting sunny highs of 13C, while Wellington is set for a top of 11C with a chance of afternoon showers.
Christchurch is tipped to hit a sunny high of 11C after this morning's frosty start before the mercury again plunges below zero for an overnight low of -1C.
Dunedin is expecting a high of 11C and a low of 3C tonight/