The return of the wintry weather after the start of spring has caused snowfall and power cuts in Wellington.
NZ Transport Agency (NZTA) regional performance manager Mark Owen says further snow flurries forecast during Thursday evening could mean road closures again.
He said conditions were changing rapidly and motorists should check before they travelled.
The Rimutaka Hill road, north of Wellington, was closed twice before being reopened again in the late afternoon.
The Desert Rd in the central North Island was reopened, with motorists being advised to take care.
Both the Interislander and Bluebridge ferries cancelled sailings because of rough weather in Cook Strait.
With snow continuing to fall across the South Island on Thursday, the NZTA said two main routes between the West Coast and Canterbury were closed.
The agency said Arthur's Pass to Otira (State Highway 73) and Lewis Pass (SH7) were shut, as was the Canterbury side of SH73 from Porters Pass to Springfield highway.
Power company Orion says fewer than 50 of their customers that lost power during the wintery blast were still to be reconnected on Thursday night after the severe storm that hit the previous night.
"Our crews will be working late into the night to restore supply to customers, but there will be a small number without power overnight," chief executive Rob Jamieson said.
Conditions are expected to ease across the country on Friday and a warmer, drier weekend is forecast.