An Antarctic storm hammering the South Island is set to unleash damaging waves on Wellington's south coast, with residents in the firing line warned to be ready to flee their homes.
The polar blast has arrived in New Zealand with force, causing flight cancellations, halting ferries and closing roads.
Wellington Region Emergency Management Office is warning that wave inundation tomorrow could be as bad as that experienced during the 2013 Matariki storm, with waves dumping debris on roads and threatening properties.
"People living close to swell-and-surf-exposed coastlines should be prepared for the likely possibility of wave overtopping and flooding of roads, potential damage to property, deposition of debris, and driftwood, sand and gravel making access difficult or dangerous, and possible road closures."
Local residents are warned to stay out of the water and arrange accommodation with friends if their homes had been impacted by past storm events.
"Prepare a 24-hour grab bag with supplies relevant to your family in case you have to leave with short notice. Move important items out of harm's way."
MetService has forecast possible heavy snow and severe winds for both the North and South Islands, as the cold air mass from the Antarctic ice shelf settles over the country.
Bitterly cold conditions are expected across most of the South Island, with the temperature dropping to 1C in Gore this afternoon and tipped to plummet to -20C in some alpine areas.
Air New Zealand has cancelled 33 flights in and out of Dunedin, Invercargill and Queenstown and the Interislander ferry has cancelled all sailings for tomorrow, likely to be extended into Wednesday.
Forecasters say the cold front will sweep northwards up the country today, opening the freezer door to all of New Zealand.
A heavy snow watch is now in force for much of the country, stretching from the deep south to the centre of the North Island.
SH94 Milford Rd and SH87 are both closed due to heavy snow, while in the North Island SH56 between Opiki and the Manawatu River Bridge is closed due to flooding.
Photos of the South Island show roads and hills coated in snow.
A road snowfall warning is now in place for the Napier-Taupō Rd, Desert Rd and Remutaka Hill Rd in the North Island along with a number of alpine passes in the south.
Warning for central North Island motorists
Waka Kotahi has urged motorists driving on SH11/Desert Rd and SH5 Napier-Taupo Rd overnight and tomorrow to take care as snow showers are forecast for the higher parts of the Desert Rd tonight to until around 7am tomorrow.
Significant snow is expected from late Tuesday morning until Tuesday evening.
Waikato system manager Cara Lauder encouraged drivers to be prepared for winter driving conditions, including snow and ice.
Further road closures were possible and motorists were urged to plan their journeys ahead and drive to the weather conditions.
"Maintain a greater following distance between your vehicle and the one in front, slow down and be prepared for unexpected hazards.
Horowhenua: Water supply critical
The Horowhenua District Council has pleaded for thousands of residents in Levin, Tokomaru and Shannon residents to reduce or stop using water immediately, or risk running out.
Due to the most recent rainfall event, the water treatment plants located in Levin, Shannon and Tokomaru have been struggling to effectively treat the muddy river water for the region's drinking water supplies.
"If residents don't act to reduce water usage or stop completely if they're able, there is a real risk that the water supply will run out and the community will need to rely on bottled water or water tanker supplies to service their minimum requirements," the council said.