MetService has issued severe weather watches for parts of the North Island and the South Island on Wednesday.
Heavy rain is forecast to pelt up and down the country with the heaviest falls expected about Nelson and the Richmond Range, North Taranaki, Tongariro National Park and Bay of Plenty.
Substantial rainfall of up to 70mm in the next six to 12 hours is also expected in Northland, Auckland, Coromandel Peninsula, Waitomo, Taumarunui and the Tararua Range.
Forecasting radars show the North Island will be blanketed by the wet weather for much of the day heading into Thursday.
MetService has also issued a warning that strong winds will blast around parts of the North Island.
Auckland can expect gusts of up to 100km/h, especially about the Hauraki Gulf and Great Barrier Island until the late afternoon.