MetService is warning of heavy rain for the Bay of Plenty and South Island's Westland Ranges.
The weather forecaster says 90-120 millimetres of rain is likely to fall over Bay of Plenty between Saturday night and Monday morning, with the heaviest falls expected on Sunday afternoon.
Up to 160 millimetres of rain is possible in areas east of Rotorua.
MetService says rivers and streams may rise rapidly and driving conditions may become hazardous because of flooding.
It says the South Island's Westland ranges could receive up to 90 millimetres of rain on Sunday, and people in the area should take great care.