An icy blast overnight brought snow and ice to the lower North Island, closing the Desert Road for a time.
The road between Waiouru and Rangipo reopened at 10.45am after a queue of trucks was cleared.
Waiouru constable Grant Cooper earlier said a light dusting of snow had frozen overnight,
making for treacherous conditions on the central plateau.
"It is not a big dump, but it's pretty icy. There's not a lot traction for vehicles," he said.
Ten to 12 trucks were caught on the road, including one stuck in a ditch after sliding off the road. The stuck truck would have to be lifted out by crane, Mr Cooper said.
"Once we get these trucks cleared, then we start thinking about opening it up for other traffic."
MetService severe weather forecaster Ian Miller said the south and east of the North Island were the worst-hit areas.
"The temperature at Waiouru at the moment is still at zero," he said. "Once you get north of Mt Taranaki, Mt Ruapehu and the East Cape, it's better."
Coastal areas could expect southerly winds reaching gale-force in exposed areas, he said.
Because of the advance warning given to farmers by the MetService, the effects of the cold snap on vulnerable new-born lambs could be lessened, Federated Farmers president Charlie Pedersen said.
Farmers in the affected areas would protect their animals by putting out supplementary feed and by shifting the mobs to less-exposed areas, he said.
"You can't shift them once they start lambing, because it increases the chances of mis-mothering," he said, describing the situation when newborn lambs lose their mothers and die.
"It is the combination of snow and wind chill that causes problems."
However, once a lamb was standing up and had the birth fluids licked off it, its wool insulated it against cold weather.
"The lambs that are at risk are the lambs that haven't been cleaned up by their mothers," he said.
MetService said the cold weather was expected to ease on Saturday.
- NZPA
