Federated Farmers is advising farmers in Southland and Otago to move stock to sheltered areas before a polar blast hits the region in the next 24 hours.
MetService said a deep trough was expected to move onto the South Island tomorrow, bringing heavy rain, snow and gales.
The lambing and calving season throughout the South Island was well under way.
Federated Farmers' North Otago president, Richard Strowger said farmers need to be aware of the chill factor created by wind and rain, and should move young animals to shelter.
"Stock can normally handle one of the elements, it's that chill factor that comes along that really smacks them around.
"So they've just got get those stock to shelter, most of them will be working on that, and will have done so already."
He said it was about minimising the affect of the weather.
Mr Strowger said some snow has already fallen in the area overnight.
Meanwhile, the Transport Agency is advising that State Highway 94 between Te Anau and Milford Sound - which was closed last night because of snow - will be closed again tonight and is likely to remain closed all day tomorrow.
In the North Island, further snow is expected about the Central Plateau today, and a road snow warning remains in places for the Desert Road until tonight.