The Bay of Plenty west of Kawerau is under an orange heavy rain warning until 3.00pm today.
MetService said the region can expect 60 to 80 mm of rain on top of what has already fallen, with peak rates of 10 to 20 mm/h.
It said localised downpours could reach rates of 25 mm/h.
"Further rain is possible from late this afternoon into early Friday morning."
There is a "minimal chance" of upgrading to a red warning.
MetService said streams and rivers may rise rapidly, and there is a chance of surface flooding and slip.
"Difficult driving conditions [are] possible," it said.
A heavy rain watch is also in place for the rest of the region, about and east of Kawerau, from 2.00pm today until 9.00am Friday, 14 August.
Periods of heavy rain may approach warning criteria and localised downpours are possible.
MetService said there is a "moderate chance" of upgrading to a warning.
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