Road users are warned to drive to hazardous conditions and prepare for disruption on roads as the country is in for some wild weather.
From the top of the North Island to the bottom of the South there are forecast gale-force winds, torrential rain and snow, with MetService issuing 46 warnings and watches from Tuesday.
The harsh weather, which coincides with school holidays, is the result of a deep low moving across New Zealand, bringing with it the associated fronts which cause the conditions.
MetService is warning people that the weather will be "a significant event".
"People are advised to keep up to date with the latest forecasts as parts of these watches will likely be upgraded to orange warnings, or more areas added."
Waka Kotahi/ NZ Transport Agency advised today there are multiple road snowfall, wind, surface flooding and rain warnings across the South Island for Tuesday.
Motorists should drive to the conditions and prepare for disruption on highways and local roads, it said.
Heavy snow and rain expected in South
The Canterbury High Country is under a heavy snow and rain watch, with heavy rain expected to turn to snow above 400 metres.
Central Otago and the Lakes District can expect similar conditions.
Several roads have heavy snow watches in place between Tuesday and Wednesday. These are: Lindis Pass, the Crown Range Road, Arthur's Pass, Porter's Pass, and Dunedin's Northern Motorway.
People travelling on alpine roads through Canterbury and Otago and into the Mackenzie Basin (via Burkes Pass or Lindis Pass) and inland Otago should carry chains and be prepared for snow on the road down to 500 metres in some areas.
As it is the school holidays, Waka Kotahi advised that people check their vehicles before setting off, take warm clothes, blankets, food and water in case of road closures.
Meanwhile, heavy rain is forecast across Tasman west of Motueka, Marlborough, and Canterbury, particularly across the Kaikoura Coast.
“There may be localised rockfalls and slips across the network so please take care,” Waka Kotahi journey manager Tresca Forrester said.
Driving conditions would be hazardous in areas with peak rain intensity forecast, snow and wind.
“Share the driving, allow extra time and watch following distances across the highways,” Ms Forrester advised.
The wintry blast is being attributed to an "atmospheric river" snaking across the country. These long, thin filaments of atmospheric moisture are capable of carrying double the average flow of the Amazon River - or 200 times that of our largest river, the Clutha/Mata Au.
Around 40 atmospheric rivers make landfall here every year, with four or five classified as strong and usually hitting around summer.
The coming system could bring 100mm to 120mm of rainfall between 8pm Monday and 3pm Tuesday, with peak rates of 15mm to 25mm an hour.
North Island
Between Coromandel and Bay of Plenty people can expect winds approaching gale force and up to 110mm of rain with rates of 15mm per hour at times.
Auckland is forecast to experience gale-force winds from late this evening until tomorrow morning.
Gisborne to Hawke's Bay can expect similar conditions, with heavy rain and at the bottom of the North Island. Wellington is set to receive gale-force winds until Wednesday morning – with a chance of extension.
The Tararua Ranges will be drenched by heavy rain, and across Cook Strait, Nelson and Marlborough districts will be battered by rain and wind.
