A cold front is quickly moving in to Dunedin, with skies turning dark and the temperature rapidly dropping this evening.
Frost and ice are expected across the country as the cold front hits, with snow down to low levels in the south.
WeatherWatch said the temperature had dropped several degrees in Southland in an hour and some suburbs in Dunedin were down to 7C.
Successive cold fronts would follow over the next few days, causing temperatures to fall further.
Brief snow falls were expected this evening.
Metservice said snow was expected on Arthurs Pass, Lewis Pass, Porters Pass, Lindis Pass, Milford Rd and State Highway 1 between Dunedin and Waitati.
Up to 2cm of snow could accumulate on Milford Rd in Te Anau, with more significant falls were expected tomorrow.
Between 10-15cm of snow could accumulating on the road above 600m tomorrow, and by Friday evening snow could be as low as 200m.
At the top of the South Island, heavy rain flooded parts of Marlborough overnight and has caused surface flooding on roads.
There is flooding on State Highway 6 between Blenheim and Havelock North, according to Transport for Christchurch. A 30km/h speed limit is in place.
TfC has also issued warnings for SH63 between St Arnaud to Wairau Valley, where multiple spots have flooded.