With a band of bad weather set to pass over most of the country on Tuesday morning, MetService is urging motorists to heed warnings of heavy rain and gale-force winds.
Torrential rain has already started in Westland, Fiordland, and will move onto Otago, Canterbury and the upper South Island before dumping on most of the North Island on Tuesday.
A Metservice duty forecaster, Oliver Druce, says South Island rivers, including the Rangitata, Rakaia, and Waimakariri in Canterbury, as well as the Waitaki and Clutha in Otago, are expected to rise.
He says the worst-hit area will be along the rivers that come off the Southern Alps, where up to 500 millimetres of rain is forecast to fall.
Mr Druce says Wellington will be hit hard by potentially damaging 160-kilometre gusts, as winds sweep the east coast of the country from North Canterbury to Gisborne.