Overnight frosts were expected to drop to -4C and minimum temperatures to about -2C - the same as temperatures recorded overnight yesterday and slightly warmer than the -5.5C frosts and -3C minimum temperature recorded overnight on Wednesday.
Rotorua police are urging motorists to drive to the conditions and allow plenty of travelling time on icy roads, to avoid speeding and getting into trouble.
According to the New Zealand Transport Agency's Safe Winter Driving Resource, between June and August can be the most dangerous time of year, as wet weather, fog, ice and snow can hit anywhere at any time.
Acting senior sergeant Graham Perks of the Rotorua police said motorists needed to adjust their speeds and the space between vehicles when driving in icy conditions.
"There have been, over the past few days, a couple of road crashes as a result of the icy conditions," he said.
Emergency services were called to a crash along Tarawera Rd shortly after 8am yesterday, which was caused by the driver hitting a patch of ice.
The van had rolled and the driver was taken to Rotorua Hospital for a check-up.
Mr Perks said motorists who came across a dangerous icy patch on the roads could call *555 and alert roading officials so they could lay down some grit.
He said there were no areas of Rotorua that were worse than others but dark and bendy areas could often be icy in the mornings.
"Most roads have the chance of having some ice on them."
He urged people to take care when driving in icy conditions to avoid getting into trouble.
"Leave plenty of time for your journey, you won't have to rush and go faster."
Rotorua weatherman Brian Holden said the cold temperatures looked set to stick around.
"It was pretty cold ... it doesn't start warming up until the sun comes out."
It's the sunny, cool days and little cloud in the sky bringing the extremely frosty mornings and expect it to continue for a few days yet, Mr Holden said.
"It's just winter setting in."
However, the sunny days won't be hanging around for much longer.
By the end of the weekend, expect a few showers, he said.
"Sunday it starts to develop into showers again ... only for a brief period, though."
Frosty mornings will return by mid-week.
"There will be fine days and frosts again."
Georgina Griffiths, a climate scientist at Niwa, said they had predicted the first few weeks of winter would be extremely cold, and they were.
With neutral conditions in the tropical Pacific, much of the weather for the country would be drier this winter, with average temperatures of between 7.9C and 8.3C expected for the rest of the season, Ms Griffiths said.
Rotorua can expect the same.
"Seasonal temperatures are likely to be near normal.
"You have to remember this is the coldest time of the year."