A heavy rain and wind warning has been extended to much of the central and southern parts of the country.
MetService said heavy rain and gales are expected Wednesday and Thursday.
The rain would likely be heaviest in Westland, Fiordland, the headwaters of Otago and Canterbury lakes, Marlborough, Wellington and Wairarapa.
Severe weather warnings have been issued for those places as well as the rest of Canterbury, Buller, Nelson and Taranaki with a storm warning for the coast of the Milford Sound.
A gale warning is in place for the West Coast with 2m swells easing from the southwest but developing from the north.
There is also a severe weather watch out for Taranaki, Nelson and the nearby Richmond Range, inland areas in Southland and Otago, Westland and Buller, which could later be ugraded to a warning.
The weather agency also warned the rain would cause rivers and streams to rise, and could lead to slips and surface flooding.
There was a high risk of north to northwest gales with gusts up to 140km/h also forecast for Canterbury, Marlborough, Wellington and Wairarapa.
Later on Wednesday night, there is also the possibility of snow down to 900m in the Southern Lakes region including several skifields around Wanaka and Queenstown.
NIWA's weather service predicted up to 222cm of snow around the country by 9pm Wednesday evening.
Snow possible to 900m in Southern Lakes region Wednesday night - great news for ski fields! pic.twitter.com/u3Z7VRD6yv— MetService (@MetService) July 12, 2016
The weather is being caused by an active front expected to travel across the country preceded by a "very strong northerly flow".
There is a low risk of thunderstorms to coastal Fiordland.
The warnings mark the second bout of wintry weather within a week.
Last Friday, downpours in the upper North Island led to flooding and road closures in eastern Coromandel, Bay of Plenty and north Auckland, icy conditions caused problems in the South, and strong winds hit Buller, Westland and Marlborough.