Temperatures plummeted to near zero in parts of the country overnight as a southerly cold snap chills the country.
For the second night in a row temperatures plummeted to unseasonal levels.
Inland areas of both islands were the coldest overnight but temperatures in the main centres were also cooler than usual, MetService said.
Waiouru in the central North Island fell to 0C and Ōhakune wasn't much warmer, at 0.8C, while Tāupo was still a chilly 2.6C by 6am.
Masterton and Palmerston North were 3C and Taumaranui fell to 3.2C overnight.
Auckland Airport was at 13.2C and Christchurch a chilly 7.4C, while Wellington Airport, at 8.8C overnight, was colder than Dunedin city's 9.9C.
In the South Island, the inland towns were coldest; Gore at 2.4C and Alexandra with an overnight low of 2.5C. The coldest overnight temperature in the country was - as expected - at Mt Hutt with -4.8C.
Morning temperatures were warming only slowly as the cool southerly winds kept having an effect.
As New Zealand shivers, the UK has had its warmest winter day on record, with the Met Office recording 20.6 C recorded in Trawsgoed and Ceredigion, in Wales.
It is the first time a temperature of over 20C has been recorded in winter, the BBC reports, breaking the UK record for February, set when the temperature reached 19.7C in Greenwich in 1998.
MetService duty forecaster David Miller said there would be gradual improvement in temperatures over the next few days.
A ridge in the Tasman Sea will flow onto the country today, bringing a warmer day.
But cooler temperatures will return for many towns tomorrow and Thursday, as cold air behind a new cold front brings rain or showers to most parts of the South Island.
Normal temperatures forecast by Friday and fine and dry weather expected for most over the weekend.