Weather: 'Heatwave' warnings could be issued as New Zealand burns past 30C

Put on your sunnies and slap on your sunblock - weather forecasters are warning some areas "may reach 'heatwave' criteria".

Temperatures are expected to soar past 30C across the country on Sunday after similar searing spikes on Saturday. WeatherWatch says this could lead to a heatwave being declared.

"Temperatures nationwide are above normal on Sunday, not just by a few degrees but in many regions by over 10C as air flows from Australia and the sub-tropics combine to move down over parts of New Zealand," it says.

"Sunday in particular is well above normal nationwide with about 75 percent of the country 8C or more above normal for this time of year."

A heatwave occurs when the daily maximum temperature exceeds the average maximum temperature by 5C or more for five consecutive days. WeatherWatch's forecast shows this is possible after multiple warmer than average days.

"As for the 'heatwave' criteria, the North Island's eastern regions are the most likely candidates but there may be some other pockets here and there, including the South Island if the cooler change on Tuesday/Wednesday isn't too great," it says.

MetService meteorologist Melissa Oosterwikj says the heat is unusual this early in the year.

"Because November is the leading up to summer, all of the records are later in the month," she told Newshub.

"The fact we're getting temperatures worth looking at whether they're breaking records or not is quite significant."

But Oosterwikj adds any heatwave will be over soon.

"This particular period of warm temperatures is expected to go back to normal by Wednesday, so this isn't a heatwave we're expecting to persist for a long time."