Some motorists have been caught out by a wintry storm which is sweeping up the South Island, bringing heavy snow to many alpine passes.
Snow, sleet and high winds are forecast for most of the South Island and the central North Island over the next 24 hours, and the Lewis Pass in north Canterbury has already been closed due to snow.
Transport Agency spokesperson Lee Wright said some vehicles had run into trouble and will be freed before the road re-opens.
Earlier today, the driver of a truck and trailer unit ignored winter driving warnings on State Highway 73 over Arthurs Pass, and became stuck, blocking the highway for some time.
Snow chains are now essential in Arthur's Pass, on the Mount Cook Road and from Omarama to Tarras on State Highway 8.
MetService said Fiordland, Southland, Clutha and Dunedin could receive snow this evening and into tomorrow. Motorists are being urged to take extreme care.
Snow was expected down to 100 metres in Clutha, Southland and Dunedin this afternoon, and on the Canterbury Plains tomorrow morning.
Snow is breaching the Southern Alps and falling at Mt Cook aero, as this 11:24am shot from our webcam shows. ^RK pic.twitter.com/tI9f0fDTAh— MetService (@MetService) August 6, 2015
Snow is unlikely to fall in Christchurch but there will be cold, sleety showers.
The cold weather will move onto the North Island tomorrow, bringing snow to the Rimutaka Ranges, the Desert Road and the Napier Taupo Road.
Snow showers are expected around the Desert Road summit from this evening through to late Saturday morning. A few further snow showers are possible in that area on Saturday afternoon, followed by heavier snow showers overnight Saturday to Sunday.
MetService meteorologist Rob Kerr said the country was in for "a changeable few days", with the showery southwesterlies also bringing a risk of squally thunderstorms and hail to western parts of both islands, heading into the weekend.
He said those planning road trips this weekend should plan accordingly.
"We've got road snow warning across much of the South Island and parts of the North island too, so all those high passes along the Canterbury high country will all be affected by snow at some point in the next 24-36 hours. We've also got a road snow warning out for the Desert Road, and there might be a light dusting for the western end of the Napier-Taupo road during Saturday.
Respite from the showers that have been drenching much of the country over the past few days will come early next week as a ridge briefly moves over from the west, said MetService.