Temperatures in Hawke's Bay could reach 40C today and tomorrow, according to a climate scientist.
The weather has peaked that high only three times in the country's history - but the Bay hoped it wouldn't last for long and was on alert for a possible drought.
Dr Jim Salinger said the conditions were ripe for the mercury to reach up to the high 30s and even 40s on the eastern side of New Zealand.
"Normally end of January, start of February is when we get the hottest temperatures of summer. The atmospheric stew is set up nicely for us to get high temperatures over the next few days," he said.
A big high sitting to the east of the country combined with a large warm anticyclone parked near the Chatham Islands and the tail-end of Cyclone Oswald are all pushing up the temperatures. If New Zealand was ever going to break its record temperature, it would be now, Dr Salinger predicted.
"The conditions are set to create warm south-westerlies in the east of the South Island and southern North Island."
New Zealand's hottest temperature on record is 42C in Rangiora on February 7, 1973. The next hottest day was recorded on February 6, 2011 in Timaru at 40.3C.
But Metservice duty forecaster Ian Gall was skeptical about Dr Salinger's predictions, saying temperatures weren't likely to get above the 35C.
"We've got modifying factors in the coastal places - there's sea breezes around and those are influenced by the temperature of the sea water nearby and that's usually a cooling thing."
It normally took a north-westerly to bring the temperatures up above the mid-30s, he said.
"It seems quite reasonable to be seeing our maximum temperatures for the next few days as somewhere a bit higher from the low 30s to about the mid-30s - about 35C maybe." Alexandra in central Otago was likely to be the hottest place in New Zealand this week.
Hawke's Bay is on drought watch after receiving just half its normal January rainfall following a dry December, contrasting last year's soggy East Coast weather.
Farmland has become the driest in the country and continuing to dehydrate.
The Metservice's 10-day forecast predicted just one day of showers for the region, Waitangi Day.
NZ's top temperatures
42.4C - Rangiora, February 7, 1973
40.3C - Timaru, February 6, 2011