Last night was the coldest of the year for much of the country, with Waiouru on the Desert Road dropping to -9°C, Metservice said.
Temperatures dropped to -7° in parts of Dunedin and Otago, while it was a little warmer in Auckland, where it reached -2°.
Metservice meteorologist Peter Little said it would likely prove the coldest night of the year.
"We had a very cold southerly flow across the country over the past few days, that brought in a lot of cold air.
"As that's moved away the sky has cleared and that cold air at the surface has continued to radiate away any heat and allowed for very frosty conditions," he said.
Temperatures should drop again below zero in parts of the country over the next few nights, Mr Little said.
Federated Farmers' North Otago provincial president Richard Strowger woke this morning to a white blanket outside his window and found much of his feed frozen.
However, he said his animals are fine.
"They don't mind the cold, actually, you can get down to -20° and stock are fine.
"It's usually a mix of two elements that affect animals - when it's cold and there's driving rain as well - if it's just one stock don't get too worried."
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