A wintry overnight blast has left major South Island state highways shut on Thursday morning.

State Highway 1 (SH1) from Dunedin to Waitati is closed due to black ice. There is no detour available.

SH87 is shut from Outram to Kyeburn in Otago due to snow and there is also no detour.

In Southland, SH94 from Te Anau to Milford is closed due to avalanche risk and snow fall and is likely to be closed for most of Thursday.

Over the country, MetService had issued snowfall warnings for six highways - Napier-Taupo Rd, Desert Rd, Lewis Pass, Arthur's Pass, Milford Rd and Dunedin to Waitati.

MetService issued a severe weather watch warning on Wednesday night, saying snow would affect higher roads and passes in central and southern New Zealand.

The heaviest snowfall was expected in Fiordland, where a heavy snow watch was in force. Snow would fall to about 100 metres, and was expected to rise above 500 metres on Thursday morning.

There was a strong wind watch in place for much of the North Island as well as the South Island near Christchurch and south of Dunedin.

Aucklanders were due for a high of 16 degrees Celsius on Thursday with cloud and the odd shower.

Showers in Wellington would clear in the morning, but there could be showers scattered in the afternoon with a high of 14 degrees.

In Christchurch, cloud and occasional showers were expected with a high of 16 degrees.