The weather was "frigid" on Monday as temperatures continue to "plummet".
It was a cold night for some in the South Island, with temperatures dropping to below zero.
Twizel was the coldest place overnight, reaching -3C.
Timaru dropped to -1C and it went down to -2C in Christchurch this morning.
Kaitaia had the highest temperature on Monday morning, sitting at 13C at 6.30am.
The chill was expected to hang around for a few days, with frost in parts of the south, before temperatures improved in the latter part of the week.
Meanwhile a heavy swell warning was in place until 6pm Monday for Wairarapa - Turakirae Head to Mataikona.
Southerly combined waves were expected to reach 4.5 metres on Monday morning.
Meanwhile, boaties and surfers were being advised to stay on dry land as huge waves pummel parts of the coast.
A heavy swell warning was in place around Wairarapa, from Turakirae Head to Mataikona, until 6pm Monday.
MetService said the waves were expected to surge to between 5.5 and six metres on Sunday afternoon, easing to four metres by Monday evening.
Further around the coast, another heavy swell warning was in place for Wellington from Cape Terawhiti to Turakirae Head until 3pm Monday, with waves expected to top out at 4.5 metres.
On Sunday, "strong, sustained winds" saw the swell hit seven or eight metres off some South Island coasts, according to a MetService update.
Marine warnings were in force for nearly all of the South Island and parts of the North over the coming days.MetService said the "disturbed" southwesterly flow was set to impact Aotearoa until Thursday, with the wind gusting up to 40 knots in places - about 74km/h.
There were gale warnings for Castlepoint, Chalmers, Chatham Islands, Conway, Foveaux, Grey, Milford, Rangitata, Stephens and Bream Head to Cape Colville.
In some of those areas there would be "very rough seas", MetService said.
A strong wind advisory had also been issued for Hauraki Gulf, Waitematā Harbour, Manukau Harbour, Coromandel and Bay of Plenty, with gusts of up to 35 knots (65 km/h) expected.
