An active front across much of the South Island will bring heavy rain, thunderstorms, gales and possible flooding.
MetService severe weather warnings cover most parts of the island, with orange rain warnings starting in the early hours of Thursday for the Tasman District northwest of Motueka, Buller, Nelson and Marlborough, excluding the Sounds.
Haast Pass (State Highway 6) is closed between Haast and Makarora because of a slip.
MetService meteorologist Heather Keats said there was "pretty decent rainfall and strong winds come through the South Island overnight as expected".
The Canterbury High Country experienced "massive" 250km/h wind gusts.
"But that's a very elevated site that's quite exposed."
Other sites saw 90kmh gusts, while some areas also had 10mm to 20mm of rain hourly.
"At the moment everything's playing out as we expected as that really active front does start to track over the South Island."
The focus would then shift to central New Zealand with strong wind watches in place for Wellington and rain watches for Taranaki from tomorrow.
It would continue north to affect the whole of the North Island, Keats said.
The active rain band affecting the West Coast was expected to stall over the Tasman/Nelson area and then affect Wellington and Taranaki.
MetService said there was a moderate chance the Tasman warning would be upgraded to red, with 100-300mm of rain expected about the ranges, and more possible in localised areas.
In Nelson, 150-200mm of rain was expected, with peak rates forecast for late afternoon.
"Nelson's starting to see some heavy rain already," Keats said.
The Marlborough District Council said the forecast rain was uncertain, and the possible impact "difficult to predict".
The weather system had the potential to stall, delivering additional rainfall on Friday, leading to a more significant weather event, the council and Marlborough Emergency Management said in a statement on Wednesday.
An update would be issued by the middle of Thursday afternoon for Spring Creek township residents on the potential impact on the Wairau River, once the latest forecasts had been assessed, the council said.
Intense rain led to flash flooding in Nelson last month, which saw mayor Nick Smith renew his call for a rain radar.
With school holidays looming, Keats said: "Sunday looks amazing" while ski fields would benefit from fresh snowfalls over the next few days.
