New Zealanders are being urged to be aware of health dangers from the heatwave after the death of a woman in Christchurch.
And at the other extreme, motorists have been warned to stay alert for sudden downpours which could lash inland areas of both islands.
The Chief Coroner confirmed yesterday that a woman aged in her 60s who suffered from multiple sclerosis had died from hyperthermia after overheating on Wednesday.
• READ MORE: Thunderstorms move up the country as warm temperatures remain
People living with multiple sclerosis can struggle to control their body's temperature in hot weather.
Chief Coroner Judge Deborah Marshall said: "I feel it is important to remind people of the dangers of overheating due to the high temperatures expected in the coming days and to take all necessary precautions."
As temperatures are forecast to stay extremely high over the coming days - including in Central Otago where they could top 40C - Fire and Emergency New Zealand issued issuing a warning that routine outdoor activities could now become hazardous.
Acting National Rural Operational Manager Tim Mitchell said even driving and pulling over in long grass could have dire consequences.
"You might want to drive to the nearest river or to the beach to escape the sizzling weather, but driving in that long dry grass, the exhaust could easily ignite a fire," Mitchell said.
Mitchell urged people to be careful when operating fans in the heat.
"People will be rushing out to buy fans, plugging them in and getting out the ice to cool down, but electronics and water don't mix," he said.
"There's also the potential to overload power sockets, which could spark a fire, so please be careful."
Temperatures have soared past a sweltering 30 degrees in many areas, and are expected to get even hotter in the next week.
In an already tinder dry Wanaka, the mercury is tipped to hit 33 degrees today and climb to 34 degrees by Monday.
In Waikato, temperatures of at least 29 degrees are forecast for the next four days.
And while scorching weather is forecast for much of the country this weekend - WeatherWatch last night warned severe thunderstorms could strike in inland areas of both islands over the coming days.
Yesterday, several struck in the eastern Bay of Plenty and the Central Plateau as holidaymakers hit the road for Auckland Anniversary weekend.
But for those celebrating a long anniversary weekend in Northland, Auckland, Nelson and Buller, the weather's looking warm and mostly settled in populated areas.
Metservice meteorologist April Clark described the long weekend weather as "pretty much status quo" for the upper North Island - aside from the chance of heavy showers.
"You may be unlucky and get under a heavy one, but it's not going to widespread. On Saturday, it's looking more like western areas [are at risk]."
There was a low risk of isolated thunderstorms, she said.
And it's going to be hot.
Auckland is forecast to reach 29C today and 28C tomorrow and Monday. Hamilton will be 1C warmer than the city of sails today and the following two days.
Whangarei can expect 27C today and a pair of 26C days for the rest of the holiday long weekend. Highs in other North Island cities are also expected to hover between 25C and 28C today and tomorrow.
In South Island holiday spots, Nelson and Buller, it will be also be a mainly fine and warm weekend. There could be showers in the ranges west of Nelson, but the region will be warm - highs in the city will be 26C or 27C through the long weekend.
"The high temperatures are sticking, just like your clothes."
The West Coast, with sunshine and a high around a more comfortable 25C, was the pick of the country, she said.
Highs in Christchurch and Dunedin will hover around the mid 20s also, but inland areas, such as Queenstown and Wanaka, can expect the baking hot temperatures of the low 30s to continue.
And WeatherWatch head analyst Philip Duncan says some areas of Central Otago could actually hit 40C early next week. Those taking shelter in the shade could expect temperatatures in the high 30S.
Nationally, Duncan described the long weekend as a "holding pattern".
"It's very much Groundhog Day with morning cloud and drizzle patches here and there in coastal areas, and then afternoon downpours with thunderstorms, some severe, inland in both islands, and that goes right through till Sunday."
But generally the rest of the month looked pretty good for most.
"With anniversary weekend, there'll be a lot of people happy that Monday is looking hot and mostly dry."
Auckland: Sunny spells, isolated showers. 29C.
Hamilton: Few afternoon showers, chance of thunderstorms. 30C.
Wellington: Cloud clears, fine. 25C.
Christchurch: Morning cloud clears. 25C
Auckland: Mainly fine, chance shower. 28C.
Hamilton: Mainly fine, chance afternoon/evening shower. 29C.
Wellington: Cloud morning and evening. 25C.
Christchurch: Mainly fine. 26C.
Auckland: Fine. 28C.
Hamilton: Fine. 29C.
Wellington: Early cloud clearing. 27C.
Christchurch: Morning cloud clearing. 25C.