Snow is falling in the South Island, with weather warnings and watches issued across the country.
An intense cold snap is heading north over the country until Thursday bringing unseasonably low snow to the South Island and lower North Island with it.
South to southwest gales are also possible, especially in the east from Invercargill to Wellington.
MetService said "significant disruptive snow" is likely to affect many areas.
Heavy snow warnings have been issued for Banks Peninsula, Southland, Stewart Island, Clutha, Dunedin, Central Otago south of Alexandra, the Southern Lakes District south of Queenstown, and Fiordland from Te Anau southwards until Thursday morning.
Heavy snow watches remain in force for the south and east of the South Island and Wairarapa including the Tararua Range south of Mount Bruce, and the eastern hills of Wellington.
Marlborough south of the Clarence River, the Canterbury High Country and foothills, North Otago, Central Otago from Alexandra northwards, and the Lakes District from Queenstown northwards are expected to see a burst of heavy snow until midnight Wednesday.
The heavy snow watch in Canterbury coast and Plains, including Christchurch, has been lifted.
MetService has also issued road snowfall warnings across the country.
"This event has the potential to impact transport, livestock and crops," MetService said.
Images show snow falling in the Canterbury towns of Fairlie and Geraldine on Wednesday morning.
NIWA principal scientist Chris Brandolino told AM on Tuesday New Zealand is going to experience an "unusual cold snap" over the coming days.
"As I say, if this were July, this would be noteworthy - but the fact that it is October is especially noteworthy," he said.
Brandolino said Christchurch could have October snow for the first time since 1969.
NIWA said both people and livestock are at risk of hypothermia - so time to get the winter woollies back out.