Snowfall closed state highways on both North and South Islands on Tuesday.
Many households in the South Island's biggest cities woke up to white backyards and road warnings in the biggest low-level snowfall of the year.
The surprise dump comes after the country's warmest and wettest winter on record.
Metservice meteorologist Dan Corrigan said the spring snowfall wasn't particularly unseasonal.
"September is still a cold month in New Zealand. We do get these wintry outbreaks that come up from the Antarctic," he said.
"It's air of Antarctic origin, brining up a showery, wintry air mass to snow at low levels including Christchurch and Dunedin ... definitely a very wintry start to the day."
Dunedinites have posted pictures on social media of snowmen and tobogganing, while news outlet Stuff documented a string of cars that slid off the road in unexpectedly icy conditions.
Towns in North Canterbury and Christchurch's northern suburbs are also dealing with the snow, the first fall in a few years.
In the capital Wellington, elevated suburbs reported flurries, while those at lower altitude are experiencing icy hail.
Farther north, snow has closed roads in the central high area around Taupo.
The cold snap is a shock after the record warmth during winter.
Climate science agency NIWA last week confirmed a record-breaking year, meaning New Zealand's three warmest winters have occurred in the past three years.
The nationwide average temperature was 9.8C between June and August, 1.4C above the 1981-2010 average.
New Zealand's seas are also enduring warmer temperatures, with "persistent marine heatwave conditions".
The weather patterns have delivered bumper snow to South Island ski fields, while starving those on North Island.
Frustratingly for operators on Mount Ruapehu, this week's weather has failed to deliver the snow they need to kickstart their worst season in more than a decade.
11°C