Temperatures are starting to plunge as storms bringing snow and huge swells, which are expected to reach up to 7.5m, rolled on to the country.

Earlier today snow began falling, ferries for tomorrow were pre-emptively cancelled and wild weather disrupted flights as a southerly change made its way north.

In Christchurch, temperature at the airport plunged 6C to 8C in just 15 minutes as school finished. Further north in Kaikoura, it dropped from 12C to 7C in the last hour, MetService duty meteorologist Josh Griffin said.

"It's going to be slowly making its way over the country overnight."

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State Highway 94 Hollyford Valley Rd to Gulliver River Bridge in Fiordland National Park closed this evening due to snow, but was likely to reopen some time tomorrow morning, a spokeswoman from the Christchurch Transport Operations Centre said.

Snow closed a road in Fiordland National Park tonight. Photo / Supplied
Snow closed a road in Fiordland National Park tonight. Photo / Supplied

In Dunedin, fans were preparing for tonight's derby between the hometown Highlanders and the touring British & Irish Lions.

They'll need to be wrapped up, with temperature expected to be around 5C, with some showers possible after the 7.35pm kick-off.

NZTA earlier warned anyone heading to the game tonight or home afterwards to be careful on the roads. It posted a warning on Facebook that there was snow expected on State Highway 87 down to 300m.

Further north, tomorrow's Interislander ferry sailings have already been cancelled due to "exceptionally poor" sea conditions.

Interislander general manager operations Mark Thompson said the Cook Strait sailings were cancelled because of predicted 7.5m waves.

The last ferry to sail from Wellington will leave at 8.30pm today, with the return sailing departing from Picton at 2.30am tomorrow morning.

At this stage sailings are expected to resume at 6.30am on Thursday.

Air New Zealand earlier today warned passengers high winds in Queenstown may affect flights, and recommends people keep an eye on the website to see if their flights are delayed or cancelled.

Several flights between Auckland and Queenstown and Dunedin were delayed, and a flight between Auckland and Tauranga was cancelled.

Three flights into Christchurch were also delayed.

Strong wind warnings are out for Wairarapa, Hawke's Bay, the coastal parts of Southland, Clutha and Dunedin, Nelson, Banks Peninsula, and the Port Hills of Christchurch.

Severe gales with gusts up to 120km/h are forecast and expected to arrive late tonight in Wairarapa and Tararua, and in Hawke's Bay south of Hastings around dawn.

In the deep south, southwest gales gusting 120km/h are expected to affect coastal areas between Bluff and the Otago Peninsula, as well as Banks Peninsula, through to mid-morning tomorrow.

Meanwhile the Coronet Peak Facebook page has put up a video of snow coming down thick and fast at the ski field.

Ski area manager Nigel Kerr said the snowfall was getting everybody incredibly excited.

"It's looking really good out there. In the last couple of hours the temperature has dropped so we can start snowmaking again to add to what mother nature is currently delivering.

"Over the next 24 hours the snowmakers and groomers will be working hard to top up the base and move it to where it needs to go.

"The weather system looks set to continue to blast us for the next 24 hours, which is great for us to increase the base."

Queenstown Lakes District Council is warning on social media that snow is falling on Crown Range Rd, saying drivers must have snow chains fitted between Eastburn Rd and Chain Bay One.

There are also reports of surface flooding on Cardrona Valley Rd.

Snow is forecast on numerous roads, including the Desert Rd, Lewis Pass, Arthurs Pass, Lindis Pass, Haast Pass, Milford Rd, and the Dunedin to Waitati Highway.

The MetService has also warned of huge swells around the country. The swells of 6 or 7m are due to move up the country as the day goes on, and are not set to ease until Thursday.

Meteorologist Tuporo Marsters said the swells were "quite significant", especially coupled with the strong winds.

There could be some coastal erosion and disruption to shipping, he said.

NZTA is also urging road users to take care on South Island roads.

A graphic released by the MetService shows lightning strikes around the West Coast and bottom of the South Island.