Heavy snow falls and ice have closed the Lewis Pass and Invercargill airport, and have led to warnings for all motorists on all alpine roads tonight.
WeatherWatch head weather analyst Philip Duncan said the worst weather was hitting the western coastline of the country.
"Some really big showers are coming in tonight for all the West Coast of the South Island and pretty much the whole west coast of the North Island.
"There will be especially heavy showers around Taranaki, King Country, Waitomo, Waikato - for those areas is looks like there's some pretty big showers coming in right now."
Mr Duncan said a lot of people don't realise it but places like Greymouth, Westport and Hokitika often share the same temperatures as New Plymouth and Auckland. They were hovering around four or five degrees this afternoon, which he said is "incredibly rare."
"The West Cost has had some of the most brutal weather this winter by a mile. They have had unbelievably cold weather for an area that is quite temperate and mild usually."
Mr Duncan said the bad weather is being caused by a winter cyclone off the coast of Stewart Island which will bring heavy snow down to sea level in some parts of Southland.
He said there is also "quite a high confidence of hail" around the west coast of the entire country including Auckland, Hamilton, New Plymouth, Wanganui and Palmerston North.
Christchurch has been protected by the hills around central Otago and south Canterbury which have acted as a "big wall" stopping showers, said Mr Duncan.
Dunedin is also forecast for a cold night and snow falls.
Josephine Shepard from Stewart Island's South Sea Hotel said despite the winter cyclone off the coast, the island's residents have been relatively spared from the bad weather, "that storm that happened last night didn't really affect us at all."
Ms Shepard said there had been some ice and hail but no snow yet.
Emergency Management Southland has warned residents via Twitter to stay indoors and prepare for power outages.
The Automobile Association's Traffic road watch service has listed more than 100 current incidents in the South Island.
The New Zealand Transport Agency has advised motorists that Lewis Pass, SH 87 Outram To Kyeburn and SH 94 Te Anau To Milford Sound (Knobs Flat To Milford Sound) are all closed due to snow.
Drivers are advised to carry or use chains and there are restrictions on towing vehicles on Haast Pass, Arthurs Pass and other alpine roads.
Otago drivers are being told to look out for black ice and to drive with caution.
A spokeswoman for Invercargill police said there had been only one accident caused by the weather so far, which involved a car skidding off to the side of the road.
The heavy snow falls have created an ideal backdrop for the Queenstown Winter Festival, midway through the 10-day celebrations.
Snow sports fans at Coronet Peak this week saw Australian reality TV host Lara Bingle and New Zealand model and professional snowboarder Hayley Holt hit the slopes for Bingle's new reality television show.
Ms Bingle's entourage said she enjoyed her time in the Wakatipu area filming for Air New Zealand. The airline's campaign is aimed at enticing "Kiwi sceptics" from across the Tasman and make them fall in love with the country and its offerings.
Additional reporting by the Otago Daily Times