MetService warns there could be further snow showers affecting both the Desert Rd and Rimutaka Hill Rd until Saturday night.
Snow had already started falling down to 1000m across the North Island and is likely to drop to 700m overnight as the freezing level lowered.
MetService forecaster Tom Adams said the Tararua Ranges were already getting snow showers down to 800m and freezing levels would lower to 300m during the day.
This week's polar blast, that left inland areas of the South Island under a fresh blanket of snow, today caused major traffic woes across the south, with vehicles slipping uncontrollably on ice-coated roads.
Snow, ice and flooding after affecting a number of highways across Canterbury to Southland. The NZ Transport Agency said while all alpine passes have remained open, the wintry conditions were proving challenging for motorists.
Police issued a warning to all road users saying the cold snap had left southern roads in a dangerous condition and pleaded with motorists to drive carefully.
Treacherous conditions were causing problems for many drivers particularly around Invercargill and on the Clinton Highway between Gore and Balclutha.
In one lethal icy patch five trucks and cars slid off the same stretch of road north of Invercargill.
With the South Island weather set to improve across the day, the north was preparing to bear the brunt of heavy rain and snow set to lash southern and eastern districts.
Wellington, Wairarapa, Hawke's Bay and Gisborne were all bracing for a stormy day with southerly gales and rain to lash the regions.
The rain has now eased in North Otago, still recovering from last week's floods, and all snow warnings had been lifted. Snow flurries fell across the Christchurch Port Hills this morning and were also forecast to fall on the Dunedin foothills today.
The Inland Route between Mt Lyford and Kaikoura was closed overnight by snow and flooding affected State Highway 1 at Dunsandel south of Christchurch.
