The Severe Weather Watch for the Bay of Plenty has been upgraded to a warning.

Metservice issued an urgent release this morning warning people of heavy rain in the region from today.

The released stated a complex trough, with a series of lows moving south over the Tasman Sea, was directing a moist northeast flow over northern and central parts of New Zealand.

A prolonged period of rain is expected about much of the North Island and northeastern parts of the South Island over the next few days.

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The Bay of Plenty was expected to experience the "heaviest falls" with more than up to 200mm of rain expected in the Western Bay and Coromandel.

People are advised that these rainfalls can cause rivers and streams to rise rapidly, surface flooding, slips and make driving conditions hazardous.

The warning comes after a Severe Weather Watch was issued yesterday for the region.