A polar blast will sweep across Aotearoa this week leaving the whole country shivering in single digit temperatures, with snow forecast for the lower half of the North Island.

From Tuesday a polar vortex will hit, sweeping up the South Island. MetService is warning of snow and "bitterly cold" temperatures which could damage crops and stress livestock.

Snow is forecast to fall in a number of main centres across both islands.

A heavy snow warning is in place for Marlborough, Canterbury, Otago, Southland and Firodland from 11pm tomorrow to noon on Thursday.

MetService warns snowfall above 400m could approach the warning criteria.

Snow should clear in inland Canterbury overnight on Wednesday, but it may continue on Banks Peninsula through to Thursday afternoon.

Weatherwatch.co.nz today said snow was forecast to briefly fall in Wellington's hilltop suburbs, Wairarapa and Hawke's Bay and the central North Island and parts of Taranaki.

"For some of these places the snow may only briefly fall mixed in with rain, especially below 250m.

"Sleet is also highly likely to sea level for a time in the lower half of the island, from Wellington to Wairarapa to Hawke's Bay. Snow flurries may also fall very near to these centres, if not directly over them."

The heaviest snow will be around the Central Plateau and the southern and eastern ranges.

There was a high chance snow would see many South Island roads closed on Tuesday.

On Wednesday and Thursday snowfall was expected to reach warning levels for the deep south including Dunedin and North Otago.

Although Christchurch will be warmer on Tuesday with temperatures in the high teens expected, it is forecast to drop to 11C on Wednesday and then -1C on Thursday morning.

Further north in Wellington, the cold blast of wind will see overnight temperatures drop to 2C and daylight highs of just 8C.

MetService meteorologist John Law told the Herald that the cold southerly wind will make this feel even colder.

The capital could even see snow in some places, and winds of up to 100km/h will blast the region. Rain could cause even more slips after 20 fell over the weekend.

The cold blast will reach all the way to Auckland, with overnight temperatures of 2C to 3C and day temperatures of 13C.

Although it will be freezing cold, the bitter weather will be over quickly – by Friday much of the country should start to warm back up to more seasonable temperatures – especially in the South Island.

These warm temperatures will continue over the weekend and into next week.