Parts of Hawke's Bay and Marlborough shared today's top honours for the hottest places in the country, nudging up and over the mid-30 degree mark.
The heatwave is being powered by hot air flowing over the warmer-than-usual Tasman Sea and unloaded above-average temperatures throughout New Zealand.
Napier and Hastings took honours today with temperatures as hot as 37C, meanwhile, 36C was recorded in the Marlborough Sounds.
WeatherWatch NZ analyst Philip Duncan said the higher temperatures were recorded in sheltered areas, not across the whole region.
Yesterday afternoon, Central Otago resident Wanda Jaggard recorded a sweltering 48C at her house in Lauder near Alexandra.
However, Jaggard was quick to point out the temperature gauge is fitted on the external wall of the house, exposed to full sun and no wind.
MetService meteorologist Angus Hines said the same stale, settled weather which is being experienced by most in New Zealand will continue this week.
"Pretty much everywhere in the country is at its average temperature, most places being above their average temperature," Hines said.
"There's been a couple of places where it's been cooler than others because there's a few areas of cloud lingering around New Zealand.
"Particularly, Kapiti Coast and Manawatu north of Wellington - it's been quite cloudy there so they haven't had the heat from the sun."
The same sort of temperatures experienced today around the 30C will be experienced again tomorrow. However, the hottest places will shift.
Eastern locations which were New Zealand's hottest temperatures yesterday and today will drop slightly in temperature, Hines said.
"The areas that are going to be the hottest tomorrow are going to shift a little bit, some of those eastern spots are going to get an onshore flow," he said.
"The wind coming off the ocean will make things a few degrees cooler but they'll still be hovering in the high 20s to the low 30s.
"Some of the warmer spots are more likely to be inland, we're forecasting for Taumarunui and Te Kuiti both looking at a maximum of 34C."
Richmond near Nelson recorded the warmest minimum temperature ever in New Zealand, Niwa said earlier today, with 24.3C recorded.
This was the warmest minimum temperature for the region since records began 157 years ago. The previous record was 23.7C.
The weather can be defined as a heatwave because a number of places in New Zealand meet the threshold, MetService meteorologist Tui McInnes said.
As defined by the World Meteorological Organisation, five consecutive days with maximum temperatures 5C above average is a heatwave.
MetService meteorologist Amy Rossiter said warm temperatures were expected over summer, but the length of the extremely warm period was unusual.
"Some parts of the South Island might only get six days over 30C in a year, and this week they could get five or six days in a row," Rossiter said.
The warm air mass is forecast to stick around until Thursday before a front moves up the country on Friday, bringing cooler temperatures.