Heavy snow has closed several South Island roads, with ice and black ice causing treacherous driving conditions on others.

Photo: Supplied: Otago District Council

Wintry weather is sweeping the country, with snow falling over the southern South Island and much of Canterbury since early this afternoon.

Snow is being forecast as far north as Marlborough, to as low as 100-200m in the far south and 200-300m in Canterbury.

State Highway 8 from Omarama to Tarras and Fairlie to Lake Tekapo and State Highway 85, Becks to Wedderburn, are both closed due to snow.

Drivers are being urged to take extra care on the road, with warnings in place for more than a dozen South Island roads, due to snow and ice.

A bus carrying 10 people crashed in the snow on Haast Pass at about 6.15pm this evening, 15 kilometres north of Makarora.

Police said none of the passengers were hurt, but the bus was stuck - possibly on its side - and contractors were trying to tow it out.

Snow has been falling on the Crown Range Road in the Otago high country and chains are needed.

Snow has arrived in Queenstown and settled down to ~500m. pic.twitter.com/FDCQpk50A2 — NIWA Weather (@NiwaWeather) July 11, 2017

In Queenstown, police warned of black ice on the roads and said one car had crashed. Flights into and out of Queenstown Airport were delayed until midday because of ice on the runway, nut normal operations have now resumed.

Photo: Supplied

Snow is forecast this evening for the Kaikōura inland road overnight, and NZTA said if it needed to be closed tomorrow, SH1 south of Kaikōura would open during the day.

Weather commentator Richard Green, in Queenstown, said inland areas of mid- and north Canterbury were in for heavy snowfall.

Hanmer Springs could get up to half a metre of snow.

"It's a wintry outbreak but it doesn't appear to be anything extreme at this stage," he said.

Photo: @NZArmy

MetService said the front would move further up the country and settle over the Wairarapa on Wednesday, bringing further snowfall to elevated areas like the Rimutakas.

In the North Island, snowfall warnings are in place for the Napier-Taupo Road, the Desert Road and the Rimutaka Hill Road, with snow predicted from tomorrow morning through to Thursday.

Hi-res snow 4cast for the North Island this time with the right labels Thanks @Laintal pic.twitter.com/U7q3Az5vwb — NIWA Weather (@NiwaWeather) July 11, 2017

Interislander has cancelled its Cook Strait ferry sailings from Wednesday night because of predicted waves of 5-7m on Thursday.

MetService has also issued warning of gales in Cook Strait from later today.

Farmers in the hill country and foothills of mid and north Canterbury were preparing for heavy snowfall. MetService said Otago and Canterbury high country stations could get heavy snowfalls.

Compare the effective temp (or "feels like" temp) across NZ today vs Wednesday. Much more blue+white (cooler!) on the map tmrw. Bundle up! pic.twitter.com/5yJDGbWPlK — NIWA Weather (@NiwaWeather) July 11, 2017

Dunedin power pole replacements postponed

An Otago power lines company has cancelled all planned power outages tomorrow due to severe weather warnings.

Aurora Energy, which is on a tight schedule to replace more than 1000 failing power poles, has come under fire for going ahead with outages of up to seven hours during the cold weather while it replaced the poles.

The company earlier cancelled today's planned outages in Dunedin suburbs, and announced this afternoon it would not proceed tomorrow either.

However the company is warning people to be ready for unplanned power outages as bad weather approaches.