Huge swells are hitting the West Coast, with the MetService urging caution around beaches as the wintry blast sets in.
Motorists were forced off the road in central Otago on Friday as snow fell fast, with more predicted at low levels in Otago and Southland over the weekend.
Forecaster Sarah Garlick says the front will affect Southland, Westland and central Otago most of Saturday morning.
"The lower South Island, we're forecasting snow to near sea-level. There could be some falls to about 200m, so definitely down there it's going to be pretty cold."
Heavy rain, thunderstorms and hail are also expected. The front is forecast to move up through the North Island tomorrow.
"We should see that front move through the lower South Island late Saturday, and onto the North Island during Sunday," said Garlick.
The air is straight from Antarctica - 72 degrees south of the equator.
"This is the coldest we have had this winter," meteorologist Stephen Glassey told Stuff. "We haven't seen any snow to anywhere near sea level yet and this will be the first time it gets close to that."
July was the hottest worldwide on record, and the New Zealand winter has been relatively mild so far - but WeatherWatch predicts August will be unsettled and cold, despite Saturday marking the end of the 'solar winter'.
"These dark 12 weeks don't always align with the coldest weather," said forecaster Philip Duncan. "In fact, after the solar winter finishes we often get some of our coldest blasts, peaking up until the mid to end of August."
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A "brief warm-up" next week is likely to be followed by another "big polar snap", he said.
"It doesn't appear New Zealand is getting an early spring this year - just a very late and probably very short winter."