A polar blast "colder than the North Pole" is set to sweep the country, with windchill set to plummet as low as -20C.
Temperatures across the country start to drop markedly from Sunday night as the cold front heads northwards on Monday.
And as well as the freezing weather, it means gales, heavy rain and heavy snow.
The cold air started off the Antarctic Ice Shelf and is travelling up the Southern Ocean to hit later tonight.
"This is an Antarctic blast and southern New Zealand is most exposed - although all of New Zealand will have a temperature drop," WeatherWatch warns.
"The coldest air arrives on Monday, especially Monday PM with temperatures really dropping on Monday night and into Tuesday morning across the South Island and into the North Island. The coldest air reaches northern New Zealand on Tuesday PM/Wednesday AM."
Weather risks
Gales and windchill
Strong wind watches are being issued around the country as the polar blast brings freezing cold gales - with a windchill of -20C forecast through the Southern Alps.
"Severe gale south to southwest winds are possible near the South Island's east coasts, also Wellington and coastal parts of Wairarapa and Hawke's Bay south of Napier on Tuesday. There is moderate confidence that a strong wind warning will be required for these places," MetService says.
Coastal parts of Southland and Otago will have windchill down to -5C, and higher elevation farms in Northern Southland and Otago could see -10C.
This is colder than the windchill the North Pole is experiencing right now, with a summer season windchill of around -6C.
For the southern half of the West Coast the angle of attack for winds may force some valleys well below zero with windchill.
WeatherWatch warns the windchill may be a danger for southern farmers with livestock exposed to sub-zero daytime temperatures around Southland and Otago and potentially Canterbury's high country.
Snow
Snow will fall across both main islands with Southland, Fiordland and Otago most exposed, along with the Central Plateau and the highways in these regions.
"Some sea level snow flurries [are] possible in Southland and Otago - although only low accumulation is expected at sea level (if any at all)," WeatherWatch says.
"Higher up, snow becomes heavier with around half a metre possible on the ranges. Farms most exposed to snow that may settle and accumulate will be over 100 to 200m with heaviest falls likely above 400m.
"Totals vary from less than 1cm in low lying areas to 50cm on the ranges."
Waves
MetService says heavy swells will cause problems around many coasts over the next few days.
"People in the capital need to be aware that southerly swells are forecast to rise to 6 metres Tuesday morning easing a little Wednesday evening. These swells will also have long periods of around 16s."
