Heavy snow was expected to hit the central North Island on Tuesday night as an icy blast moves up from the south.
MetService forecaster Erick Brenstrum said up to 20cm could blanket the hills above 800 metres between northern Manawatu and Hawke's Bay.
The snow could make roads dangerous and the accumulated weight of snow drifts could damage trees, powerlines and weak structures, he said.
The Desert Road between Rangipo and Waiouru in the central North Island closed late on Tuesday night. Detours are in place via State Highways 46, 47, 4 and 49. Snowfalls were also likely to affect the Rimutaka Hill Road between Wellington and Wairarapa.
In the South Island, many woke up to snow in Southland, Otago and Fiordland.
Snow began falling in Dunedin about 6am, settling in the higher suburbs including Brockville, Halfway Bush and Mount Cargill. Police said they dealt with dozens of incidents on Tuesday, including minor crashes and abandoned cars blocking roads.
The snow flurries and sleet are forecast to ease in Otago and Southland overnight, although roads would still be treacherous with ice for a couple of days. Falls were also likely to affect higher roads in Canterbury.
In the alpine region, up to 10cm was expected to fall on the Milford Road in Fiordland between 2pm and midnight. A similar amount was expected on the Lewis Pass, while the Lindis Pass was likely to get 4cm and the Porter's Pass 7cm.
The New Zealand Transport Agency said motorists should carry chains and drive to the conditions. Drivers of caravans, campervans and other high-sided vehicles are urged to take care on a number of South Island roads due to high winds.
State Highway 87 Outram to Middlemarch and State Highway 94 Te Anau to Milford Sound are closed overnight on Tuesday.
Queenstown police said snow covered roads caused two accidents in the region, but no one was injured.
Some flights were cancelled in and out of Queenstown Airport on Tuesday.
Previous bad storm
There was extensive snow in Southland and parts of Otago in September 2010.
Federated Farmers said it was the worst storm in almost 40 years. The last time there was anything as severe was in 1972.