Heavy snow is forecast throughout the South Island on Saturday night and Sunday to low levels.
Temperatures fell to minus seven in Ranfurly on Friday night and MetService warns it's about to get colder still.
MetService says a cold southerly change from Antarctica will bring heavy snow and below freezing temperatures to Southland, Otago and inland Canterbury.
Coastal areas can expect sleety snow showers and wind chill across the South Island. Farmers in inland parts of Otago and Canterbury are advised to move stock to shelter.
Forecaster Gerard Barrow says temperatures during the day are unlikely to lift above five degrees.
He says the cold snap will move onto the North Island on Sunday and Monday, bringing snow to State Highway 2 (the Rimutaka Hill road), the Desert Road (State Highway One) and the Napier-Taupo road (State Highway Five), before moving west.