Metservice meteorologist Cameron Coutts said it was an abnormally hot night for places across the country, including Wellington, where temperatures stayed above 20C – 7C warmer than usual for this time of year.
Aucklanders also experienced a warm night with temperatures 4C hotter than the 16C average for January.
It was marginally cooler in the South Island, but many places still logged overnight lows in the high teens.
The scorching temperatures were set to continue for the next three to four days when most places in the North Island would be 20C or hotter overnight.
Coutts said temperatures were set to hit 33C in Alexandra today, while Hawke's Bay, Gisborne, Marlborough and Christchurch were in for a toasty 30C.
A high of 27C was forecast for Auckland.
It would be a fine day for most apart from a few showers along the western side of the country, which were set to continue tomorrow.
A system sitting out over the Tasman Sea would see cloud increase over the North Island tomorrow and bring rain to Northland by evening.
The east and south of the South Island were in for cloud and a bit of drizzle on Sunday.
