MetService says a cold snap that hit overnight has brought blizzard-like conditions.
A severe weather watch is in place for Fiordland, Southland, Otago and Canterbury for strong southwesterlies and snow down to sea level.
Snow has been falling in south Otago and in Dunedin's hill suburbs.
MetService said the combination of strong winds and snow showers would create blizzard-like conditions, with 25 to 30cm of snow expected in areas above 300 metres over a period of 24 hours.
The combination of strong southwesterlies and snow showers was likely to bring blizzard conditions, putting livestock at risk and possibly disrupting transport.
The weather watch also warned of the possibility of severe gales in coastal Otago and Banks Peninsula, from midday on Sunday until late Monday morning.
Meteorologist Ciaran Deelin said Southland and Otago would be the worst hit, and farmers there had been preparing for the bad weather.
"In the 24 hours from midnight (on Saturday) through to midnight Sunday above 300 metres we're expecting 25 to 30 centimetres to accumulate."
Snow was expected for most alpine passes including the North Island's Desert Road until late Sunday evening. Motorists are advised to check conditions and carry chains.
The front is expected to bring frosts to many South Island areas and parts of the lower and central North Island on Monday, with the weather settling on Tuesday.