MetService severe weather forecaster Leigh Matheson said the strongest winds this morning were in the Foveaux Strait, Stewart Island and Southland.
The Foveaux Strait was being battered by 100km/h winds, gusting up to 160km/h, while 60km/h gales in Invercargill were gusting up to 120km/h.
Strong winds were also hammering Otago, with 50km/h northwesterly winds in Dunedin gusting up to 80km/h.
Ms Matheson said the gales should ease this morning as the front moved over the country.
"Temperatures are expected to drop significantly from later this morning into this afternoon, so snow will gradually lower from this afternoon into this evening," she said.
In Fiordland, snow below 300m was expected from this afternoon, becoming heavy this evening. Heavy snow would follow in Southland and Clutha from about midnight.
"In all of those areas, we're expecting snow to near sea level. But the significant amounts, or the large amounts, will probably be above about 300m," Ms Matheson said.
Snow was likely to push further north tomorrow, with southern parts of Central Otago and Dunedin expected to see some snow to low levels, but not in large amounts.
Heavy rain was falling in Westland this morning, with 30-40mm of rainfall in the ranges since midnight. The rain was not expected to ease until this afternoon.
Strong winds were also expected in the lower North Island later today. The wind was already blustery in Wairarapa, with a severe weather watch for gales in place.