Motorists escaping for the Queen's Birthday long weekend are being urged to take care as a cold snap brings treacherous rain and wind and heavy snow to the South Island.

Snow could even fall down to sea level in areas, such as Invercargill.

A torrential downpour has already played havoc with Auckland commuters this morning as a series of crashes choked Auckland's motorways, causing delays and congestion.

And the rain hasn't ended. Further persistent falls are forecast in Auckland throughout the afternoon.

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The wild weather has left Auckland looking at highs of 14C and 13C on Saturday and Sunday with MetService tweeting at midday that the cold front had already sent the mercury plunging 4C.

Monday is tipped to be the pick of the long weekend weather with a break in the rain and a high of 16C.

It comes as earlybird motorists are already hitting Auckland's motorways in a bid to beat the long weekend traffic.

Police and the NZ Transport Agency were urging motorists to take care and "stay alert, be patient, and don't rush".

Police national manager of road policing Superintendent Steve Greally said more than 160 people had died on the roads this year, but many of the deaths could have been prevented if four safety actions were taken.

"Make sure everyone has their seatbelts on, remove distractions and stay focused on driving, don't get behind the wheel if you've been drinking or are tired, and drive at a safe speed for the conditions."

NZTA expects the holiday traffic heading north out of Auckland to become heavy from now through to 6pm today. Traffic is then tipped to be heavy with returning weekenders coming south into Auckland on Monday between 10.30am-6pm.

Those travellers heading south out of the city should expect heavy traffic today from now through to 7.30pm.

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Traffic heading north and south between Wellington and the Kapiti Coast is also expected to be heavy over each day of the long weekend, NZTA said.

Wellington can expect a windy and wet high of 15C today, before the temperature drops to 12C and 9C on Saturday and Sunday. Monday should be mainly fine with a high of 13C.

In the South Island, rain and strong winds were making driving treacherous on a number of roads.

"The state highway network is currently being impacted by heavy rain and strong winds, with a number of strong wind warnings across the South Island," the South Island advisory said.

As well as heavy snow falls in the mountains, MetService was now expecting snow down to 400m.

Fellow forecaster National Institute of Water and Atmospheric Research said parts of the South Island could see snow down to sea level, including in Invercargill.

Snow had already started falling in the Crown Range between Queenstown and Wanaka.

The Remarkables ski area, scheduled to open next Saturday, received 5cm overnight, while Coronet Peak - expected to open on June 15 - got 6cm.

Did you hear? Snow is coming! Here's a little bedtime update from Steve so you can dream about winter ❄️Happy Valley at Whakapapa is set to open on Saturday! Although the forecast isn't sunshine and there’s wind - there’s SNOW. If the weather allows, we’ll open for beginner skiing & riding ⛷🏂 Our base area café and Happy Valley Bistro will be open for coffee, our *new* freshly baked-on-mountain cakes, slices, and muffins 🍰 along with a new menu using locally-sourced ingredients for all our mountain foodies. Snowplay areas will only be available if mother nature delivers a large dump of the goods🤞❄️ Otherwise it will be skiing & riding only on the learner's carpet lift. It has been a bit of a warm start to the winter but we’re amped, we're ready to go and we've got all our fingers and toes crossed for it to snow, snow, snow!

Posted by Mt Ruapehu, Whakapapa & Tūroa Ski Areas on Thursday, 30 May 2019

Snow warnings were now in place for a series of mountain roads.

These included roads through, Lewis, Arthur's, Porters, and Lindis Passes as well as the Crown Range Rd and Milford Rd where snow was expected down to between 400m and 800m.

Heavy snow watches are in place for the Kaikoura Ranges and the Canterbury High Country and foothills, mainly north of Mt Cook for tomorrow.

Heavier snowfall was expected tonight and tomorrow night.

The severe weather was set to persist across much of the country, MetService said.

"So far this week has been all about heavy rain and ferocious northwest winds, but across the weekend the weather pattern shifts, and strong southerlies, cold temperatures and snow become the focal points," meteorologist Angus Hines said.

He said cold, unstable air over New Zealand had created an environment where thunderstorms and hail were possible in many areas this weekend.

While the weather would gradually improve heading into Monday, the cold southerlies would be back with two potentially destructive storms next week.