A freezing blast will make its way up the country today bringing snow to low levels and more rain to the sodden top of the country, MetService warns.
This afternoon a cold southerly push will move up the South Island, meteorologist Hannah Moes said.
"That will bring snow to low levels in Southland and will fall on Banks Peninsula during the day and possibly some sleety showers in Christchurch."
Read more: Wrap up warm as cold starts to bite
Snow could fall to about 100m to 200m.
The cold air mass was then forecast to spread north, bringing snow down to 400m on the Rimutaka Hill Road and the Desert Road later today, she said.
"We have a road snowfall warning for [the Rimutakas] with accumulations of 10cm to 20cm during today and tomorrow."
Rain-soaked Northland will not be getting a reprieve, with more showers forecast, Ms Moes said.
"A front will pass through there around the middle of the day today, so the showers will get more frequent then."
However, the rain should not be heavy.
The showers should clear by tomorrow across the North Island, but they would hang about until Wednesday in the east of the South Island, she said.
MetService meteorologist John Law told Radio New Zealand skiers would benefit from the cold snap, with snow falls expected for slopes in southern Otago around The Remarkables and Cardrona.
He warned motorists to be careful of icy patches on the roads, especially across the South Island.
Meanwhile, a slip yesterday has resulted in State Highway 1 at the Brynderwyn Hills in Northland, closing for the next several days, the New Zealand Transport Agency (NZTA) said.
Heavy rain in Northland over the weekend led to a 10-metre-long section of hill collapsing under the highway yesterday afternoon.
A cold,starry and snowy morning in Aoraki/Mt Cook National Park. -7C last night. How's it looking with you? ^JL pic.twitter.com/N5uFo6L0Om— MetService (@MetService) July 20, 2014
"Unlike the underslip on SH1 at Kawakawa last week, there is no room on the Brynderwyns to build a detour route around the collapsed section of road," NZTA's regional journey manager Jacqui Hori-Hoult said.
"We will have to repair the underslip itself before we can re-open the Brynderwyns."
The slip was still moving and a detailed assessment of ground stability would have to be completed before repair work could begin, she said.
"We are aware of the importance of this section of highway as the main road link between Northland and Auckland. Everything will be done to have it repaired as quickly as possible, but it will only be re-opened when we are completely satisfied it is safe for people to use."
Two detours were available for drivers - one via SH12 through Paparoa and Oakleigh, and the other via Waipu and Mangawhai.
The detours would add another 30 to 40 minutes to journeys, NZTA said.