Heatwave: Inland of Gisborne soars to record-breaking 40C this afternoon

New Zealand's summer scorcher just got even hotter with the mercury tipping an incredible 40C for the first time in at least 15 years.

A heatwave from Australia pushed hot air over the North Island today, sending the temperature in Te Karaka, inland from Gisborne, to a high of 40C at 4pm, according to forecaster WeatherWatch.co.nz.

The heat then slowly reduced to 38C at 5pm and was 37C at 6pm.

WeatherWatch.co.nz head forecaster Philip Duncan said this was the first time in the agency's 15 years of operating that it had observed anywhere in the North Island reaching 40C.

Temperatures soared to a record-breaking 40C inland from Gisborne this afternoon. Image / Google

Historically 40C temperatures were recorded in the eastern South Island, Duncan said.

He added that the official temperatures taken by Niwa and MetService were usually recorded at airports which were largely coastal and where the sea breeze could cause the temperature to drop by up to 10C.

"The sea breeze at these coastal locations can therefore remove over 10 degrees from the air (hence why you're always hearing of certain NZ councils and mayors railing for new observations in their city, not at the airport)."

While inland Gisborne was the only area to reach 40C today, other parts of the North Island such as inland Hawke's Bay reached mid-30s.

Duncan said temperatures would continue to remain high tomorrow before dipping noticeably by up to 10C on Wednesday.