The Army last night moved in to help rescue hundreds of motorists trapped in their vehicles after heavy snow closed roads across the central North Island.

Up to 200 vehicles were trapped on State Highway 2 between Napier and Taupo. Most were believed to have stopped because of snow and ice at Waipunga, at about the halfway point.

About 150 people had made their way to the Te Pohue Hotel and a further 60 were at the Te Pohue Hall, Hastings Civil Defence controller Mike Maguire said.

"Police, the Army and Civil Defence have activated and the Army is sending in Unimogs to get people to buses waiting at a safe point on the road," he said.

He advised those waiting to "stay where they are and stay as warm as possible."

"When they hear or see Army vehicles approaching they need to flash their lights so they can be seen."

A welfare centre was set up at Hukerere Girls College at Eskdale, and Red Cross and the Salvation Army workers gathered there to make sure evacuees were warm and fed.

The Army also rescued motorists from State Highway 1 near Waiouru.

Police central communications Inspector Kirsty Henson said about 120 cars were stuck on SH1 between Waiouru and the Three Sisters. People rescued would be returned to their vehicles tomorrow.

Snow also closed State Highway 49 between Ohakune and Waiouru, and State Highway 47 at Turangi.

Head weather analyst Philip Duncan said heavier snow was likely overnight. The cold air had also reached Waikato yesterday.

In Auckland the cold southerly failed to arrive, and the city had a high of 17C.

Today was expected to be colder, with highs barely making teens for most of New Zealand.

The MetService issued heavy snow warnings for the central North Island high country and the hills and ranges of Hawkes Bay.