Hundreds of homes and businesses have lost power as hurricane-strength winds of up to 131km/h blast the top of the country.
Storm-force gales and monster seas are beginning to batter the entire west coast in the latest wintry onslaught to hit New Zealand.
Hundreds of homes and businesses were without power at midday, as violent gales started wreaking havoc, with trees toppling and flying branches cutting power in rural areas stretching from Karaka to Waiuku.
MetService said powerful 131km/h gusts were recorded at Cape Reinga this morning, while 114km/h winds were blasting Manukau.
A Counties Power spokeswoman said the damaging winds had started causing problems across the network, with a large tree bringing down power lines and cutting electricity to scores of customers. Flying branches had caused more than a dozen smaller blackouts across the region.
On the coastline, furious seas were starting to ramp up, with banks of towering waves and frothy white caps stretching far out from shore. It's predicted that dangerous nine-metre waves will pound western seaboard of both islands, with WeatherWatch.co.nz warning of a potentially damaging storm surge.
"These are exceptionally large waves and people should avoid being too near the water," said WeatherWatch head forecaster Philip Duncan.
On top this, the upper North Island is in for a battering, with a strong-wind watch issued for Hamilton north, with gales ramping up across the day. Southwesterly gusts are expected to reach a powerful 110km/h.
Storm-strength winds started causing problems just before midday, with large trees and flying branches bringing down power lines and cutting electricity to around 400 properties across Tuakau and Pukekohe.
Fire crews were called out to clear a large tree that brought down powerlines in Tuakau and to secure a patio roof threatening to take flight in Pukekohe.
There were also thunderstorms in the mix, as well as a fresh snowfall for the centre of the island.
Meanwhile, in the south, snow was falling across inland Otago and Southland. It's expected to worsen tomorrow, descending to near sea level in the deep south.
Bitterly cold flurries were also expected to bring up to 2cm of snow on the central plateau.
A number of snowfall warnings have been issued for key alpine passes including the Desert Rd this morning.
MetService said significant swells would pound west coast beaches of both islands for the coming two days.
Waves were expected to reach six metres high, especially about Kaipara, north of Auckland.
WeatherWatch warned that towering waves up to eight metres high could slam the Manukau Heads at the harbour's entrance this afternoon.
In addition to blustery winds walloping the top of the country, there was also a risk of heavy thundery showers bringing gusts to other regions not under the alert.
The strong winds and dangerous seas were expected to ease slowly across Thursday and Friday.