Civil Defence authorities are also warning campers, trampers and holiday-makers that rivers could rise rapidly in many parts of the country and to prepare for strong winds as a moist northwesterly flow sweeps across the country ahead of a cold front.
Heavy rain is expected about the South Island's West Coast, the Southern Alps and Otago today, before spreading to the southern and central North Island.
Severe northerly gales are expected about central New Zealand later today.
Up to 300mm of rain is predicted to fall at the headwaters of Otago rivers, while Marlborough, Wellington, the central North Island and the ranges of eastern Bay of Plenty can expect heavy rain during the next couple of days.
"This heavy rain will cause river and stream levels to rise rapidly and there may be slips, surface flooding and poor visibility, making driving conditions hazardous," MetService weather forecaster John Crouch said yesterday.
In Nelson and Tasman, Civil Defence authorities have warned campers and trampers to watch out for rapidly rising streams.
However, the eastern side of the South Island is expected to dodge the worst of the weather.
"There has been nothing in the warnings that we've been getting that would indicate that level of concern," Dunedin Civil Defence and Rural Fire manager Neil Brown told the Otago Daily Times yesterday.
"We're actually looking at the rain in a positive, rather than negative, as it has been helping with the fires at Mt Allan."
On the bright side, the MetService reported the weather system was moving quickly across the country.
The first week of the new year in New Zealand is expected to be mostly sunny, settled and dry.
