The MetService has extended its rain warning for the Bay of Plenty and Taupo to Westland in the South Island.
The service says a front should move east across most of New Zealand overnight on Wednesday, bringing rain to most places.
A heavy rain watch is in place for the Coromandel peninsula and northern Gisborne, but rain in these places is expected to remain below warning levels.
Heavy rain is also expected at Mt Taranaki, northwest Nelson, Buller and northern Fiordland.
Meanwhile, the Bay of Plenty Regional Council says with catchments already saturated, river levels may rise quickly and farmers should move to stock to higher ground.
Civil Defence in the Bay of Plenty says the region's rivers are coping with rain on Wednesday night.