Christchurch could see its first October snowfall in more than 50 years.
MetService is forecasting snow down to sea level across the South Island this week, with a polar blast expected to hit the country.
Temperatures are forecast to drop on Wednesday with Christchurch in for chilly lows of -1C.
MetService meteorologist Heath Gullery says the last time Christchurch saw an October snowfall was in 1969.
In the Dunedin region, tomorrow would start with possible morning frosts, but as the northerlies changed southwesterly, showers would develop and turn to snow in the evening.
The snow was expected to lower to about 400m in the Dunedin and Southland areas, and 300m in inland Otago.
The weather was expected to clear on Thursday.
MetService said it was a "significant weather event" for October and urged farmers to be prepared for the polar blast which may bring stress to livestock.
-Additional reporting ODT