Almost every part of the country is likely to see temperatures in the high 20s and low 30s over the next week as NZ gets blasted by a heatwave.

No part of the country is likely to escape as New Zealand is set to get roasted by a heatwave making its way across the Tasman sea with temperatures expected to be in the mid-thirties.

Forecasting agency NIWA expected "some near-record or record temperatures are possible as we head through next week".

NIWA Principal Scientist Chris Brandolino said that several places around the country could see temperatures inside the top four highest temperatures ever recorded for a January in those locations.

There will also be high humidity and a persistent heat, which could make it feel hotter than it actually is.

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"You can have a bad day or two but when you get up to four, five, six days of warm temperatures plus high humidity, which can mean a bad night's sleep for those who don't have air conditioning or don't like sleeping with fans, it can start to really wear you down."

Meanwhile, Metservice meteorologist Rob Kerr said that the heat and humidity would stay until at least Friday.

"We define a heat wave as temperatures of five degrees or more above the average for that region at that time of year, for at least five days," he said.

"Ashburton is looking like it will get that, and really across most of the country you'd expect to see an average of 23-25 degrees, and most places will be in the high 20s/low 30s."

Blenheim is looking like it will see the hottest temperatures, estimates for at least 33 but possibly as high as 35 on Monday.

Some near-record or record temperatures are possible as we head through next week ♨️



Watch the heat build and reach a peak next Friday 👇 pic.twitter.com/cQbaiyj6wd — NIWA Weather (@NiwaWeather) January 25, 2019

Other hot points include Christchurch with 33 degrees on Monday, 33 for Napier and Hastings on Monday, 32 for Hamilton and 31 for Upper Hutt on Tuesday, and 33 for Masterton on Wednesday.

Nelson, Hamilton, and Tauranga are all likely to be at or around 30 degrees for the entire week, and even Invercargill and Gore could hit 29 late in the week.

"The humidity will be a big factor because it won't cool down much at night, and it will stay stuffy in the North Island until midweek," Kerr said

"Over the North Island it will be persistent because there's a lot of warm air and no wind to blow it away."

He said the temperatures are partly due to the unseasonably high sea temperatures around the Tasman.

"The hot air is getting dragged over here from Australia. Usually, the sea can change that, but right now the sea is warmer than usual, so the air is arriving to us warmer than it would usually be."

The warm air northwesterly has meant that strong wind warnings have been put in place for Canterbury High Country, Otago, and Clutha from Saturday to Sunday, with wind speeds around 120kmh expected. There is also a heavy rain warning for Fiordland.