A severe weather warning is in place for inland parts of the South Island, where heavy snow is expected to fall today.
The MetService has issued severe weather warnings and road snowfall warnings for the alpine passes.
State Highway 94 from Te Anau to Milford Sound was already closed due to snow, and State Highway 8 in Lindis Pass was likely to receive 10cm to 20cm of snow through to Wednesday night.
The New Zealand Transport Agency also advised caution because of snow and ice on the Desert Road, in the Tasman region on State Highway 60 between Takaka and Riwaka, State Highway 6 between Kawarau Falls and Lumsden.
MetService said the heaviest snow, with about 20cm to 30cm above 400m, would fall about inland parts of Southland and Otago.
Meteorologist Matthew Ford said a cold southerly front moved over the south of the country overnight, carrying rain and snow.
"This situation's sort of developing overnight. We have heavy snow warnings out for a lot of these places. It's a little early for first-hand reports of snow but I'm confident from the observations that we have that plenty of snow has been falling about inland and lower parts of the South Island."
For Canterbury south of Fairlie, 25cm to 35cm is expected above 400 metres.
He said blizzard-like conditions should be expected in exposed areas.
Chains would be required in Arthur's Pass in Canterbury between Springfield and Otira, and towing vehicles were not being allowed through.
There was further snow expected for eastern Otago on tomorrow morning, and around Canterbury as far north as Kaikoura tomorrow and Friday.
There was also a chance of bursts of heavy rain around Buller and the Tararua ranges, with falls of 50mm in six hours or 70mm in 12 hours possible.