A severe weather warning has been issued for parts of the Bay of Plenty as heavy rain drenches the region.

Heavy falls this morning are expected to continue into Friday afternoon, the Metservice states.

The Metservice warns that in the 36 hours from 3am Thursday to 3pm Friday, between 150 to 180mm of rain could accumulate, particularly about the eastern ranges.

"A front should stay slow moving over the North Island today before drifting eastwards and weakening tomorrow afternoon, bringing periods of heavy rain in Bay of Plenty.

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"This is a significant amount of rain for these areas, and people are advised that streams and rivers will rise rapidly, slips and surface flooding are also likely," a written statement read.

These heavy falls could reach peak intensities of 15 to 25mm per hour, particularly about lunchtime today.

But don't expect things to cool down. Temperatures are expected to reach a high of 26C today, with and overnight low of 21C.