Emergency services are responding to slips, flooding and fallen trees that have forced the closure of State Highway 6 between Murchison and Glenhope.
It will remain closed for some time while the debris are cleared along the 40km stretch of road in the Tasman district, police said.
Motorists are being asked to delay travel or avoid the area.
Meanwhile in Auckland, Fire and Emergency has been responding to minor weather-related incidents including fallen trees and downed powerlines.
And the MetService has issued a severe weather warning for Gisborne, the eastern Bay of Plenty Ranges and Taranaki.
Heavy rain in these areas may cause rivers to rise rapidly and make driving conditions dangerous, the agency said.
A heavy rain watch is also in place for Auckland, Waikato, Waitomo, Taumarunui, Taupō and parts of the Bay of Plenty.