Nelson has been hit by scorching weather this week with the temperature hitting the mid-30s.
Warm temperatures were expected over summer, but the length of the extremely warm period was unusual, Metservice’s Amy Rossiter says.
“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.”
Niwa said already in the Nelson region the record for the warmest minimum temperature had been broken, with 24.3C recorded in Richmond.
This was the warmest minimum temperature for the region since records began 157 years ago.
The previous record was 23.7C.
The warm air mass was forecast to stick around before a front moved up the country on Friday bringing cooler temperatures.
It also means that a total fire ban has been enforced around the region.
The ban came into effect at midday on Sunday and is expected to remain in place until the heatwave subsides.
Crews were called to extinguish multiple fires on Tahunanui Beach last week.
A person attempted to smoke out some rabbits at the beach by lighting a fire at each end of a burrow.