MetService meteorologist Tui McInnes said he wouldn't have been surprised if isolated pockets around Rotorua reached even lower negative temperatures overnight.
"Being by the lake at the airport, the Rotorua gauge usually records higher temperatures than in other areas around town."
"We are closing in on winter for sure and last night was just the perfect condition for really cold temperatures," McInnes said.
"Basically, the high country as a whole is really nippy. Anywhere inland in the South Island really and many parts of the North Island."
McInnes said motorists should be vigilant this morning, especially on alpine passes.
MetService meteorologist John Law said a wind direction shift round to the southwest was dragging cold air up and across New Zealand from the Southern Ocean.
"This cold air, combined with the clear sky and light winds last night meant our temperature could just drop away overnight.
"The good news is that, despite the cold start to the day, we will keep the clear sky through much of today and have a fine day for much of the Bay of Plenty.
"The cloudier skies over Taupō this morning should also break up to leave some long periods of afternoon sunshine," he said.
"Looking ahead, it'll be worth keeping those extra layers close to hand as we have a few more chilly, frosty nights to come as the cold air remains with us.
