Snow and ice have made some South Island roads treacherous and forced some schools to open late.
State Highway 85 from Lauder to Wedderburn, State Highway 6 from Kingston to Five Rivers and State Highway 73 at Porters Pass are affected.
There is also snow on State Highway 1 from Mosgiel to Andersons Bay and flooding on State Highway 6 from Lumsden to Castlerock.
Chains are essential on State Highway 8 on the Lindis Pass, from Tarris to Omarama, because of snow.
The snow and ice in Dunedin prompted primary and intermediate schools to open late today, because of transport issues, with the school day getting under way at 10am. However, East Otago High School and Flag Swamp Primary School were closed for the day.
Good morning cold, freezing Dunedin! pic.twitter.com/0wqU8Jv0KQ— Kenn Manasan (@kmanasan03) June 21, 2015
MetService forecaster John Law said temperatures in the South Island would plummet tonight.
"Last night we got down to about -5degC in Tekapo and I think as we go through towards Monday night to Tuesday morning, we're going to find those temperatures way below freezing across many spots in the South Island," he said.
Meanwhile, Orion operations manager Stuart Kilduff said the company was using helicopters to get line crew to Castle Hill and Lake Coleridge in Canterbury, which lost power in heavy snow last Thursday.
Power remained off to about 160 customers, with 10 crews out working on the lines this morning.
"They are big jobs, crews have to use helicopters just to get near the faults," he said.
A helicopter could also be used to restore a damaged line across the Waimakariri River, which cut power to about 40 customers in the Kowai Bush area.
In South-Canterbury Alpine Energy services manager Michael Boorer said 329 customers spread throughout the region were still without power, after snow weighed down power lines and caused them to snap.
Most customers should have their power back on by this evening but isolated areas could be without it for most of the week.
Orion customer areas still without power: Te Pirita, Hororata, Coalgate, Glentunnel, Sheffield, Springfield, Castle Hill, Windwhistle, Charing Cross, Darfield, Rakaia Gorge, Kimberley, Glenroy and Whitecliffs.
Alpine Energy customer areas still without power: Raincliff, Cannington including Burnett Road, Limestone Valley Road, Haldon, Stoneleigh Road, Clayton Road, Sherwood Downs, Godley Peak, Waihaorunga, Ashwick Flat, McKeown Road, Beautiful Valley, Langley Downs and Middle Valley Road.