The Milford Track has been closed and holidaymakers are being warned to remain alert for danger, as 2013 starts with extremely wet or windy weather for much of the South Island and the lower North Island.
More than 250mm of rain overnight had resulted in both the Arthur and Clinton rivers flooding across the Milford Track in numerous places, and the Arthur River reaching record levels, the Department of Conservation said.
High winds and poor visibility were also affecting the Mackinnon Pass.
No new independent walkers had started the track today, and those already on the track would stay in huts for a second night, DOC said.
Guiding walking operation Ultimate Hikes had continued to operate, using helicopters to move walkers when needed.
The weather pattern was expected to continue until the middle of the day tomorrow, but it was hoped independent walkers would be able to restart their operations from tomorrow morning, when another assessment of track conditions would be made.
Other walking tracks in the area remained open, but DOC urged people to assess the weather forecast, their experience and preparedness before heading into the back country.
"People are especially urged to watch out for swollen rivers and other natural hazards as a result of the poor weather. Caution is advised."
MetService chief forecaster Peter Kreft said rainfall totals on the South Island West Coast and over the Southern Alps may approach one and two-day records.
Heavy rain was spreading north along the Southern Alps and west of the South Island, and was expected to stay heavy until tomorrow.
Total rainfall could reach 500mm to 600mm in the ranges of Westland.
"Further, rainfalls in the headwaters of the Canterbury and Otago lakes and rivers may be in the region of 100 to 200mm by then, which might make this an extreme event," Kreft said.
A rainfall warning has been extended to the ranges of Buller and northwest Nelson, where between 80mm and 120mm of rain was possible in the 15 hours from 9am tomorrow, accompanied by strong northwest winds.
The heavy rain would cause rivers and streams to rise, including those in Canterbury and Otago fed from the Divide.
"The warm weather and the time of year probably mean that there are a lot of people camping near lakes and rivers in Canterbury and Otago," Kreft said.
"It's important that they are aware these lakes and rivers could rise rapidly, even if it's not raining at their camp site. And it's likely to be pretty windy down some valleys."
Severe gales would be blasting inland parts of Otago and Canterbury, as well as Wellington and southern Wairarapa today and tomorrow, MetService said.
In the east of the South Island, northwesterlies were reaching gale force in exposed places this morning and should remain strong until tonight or early tomorrow.
About inland parts of central and north Otago and inland Canterbury, severe gale gusts of 120kmh were possible. Gusts could reach 140kmh about the Canterbury high country today.
In Wellington and southern Wairarapa gusts could reach 120kmh from tonight and throughout tomorrow, possibly gusting to 140kmh tomorrow evening.
"Winds of this strength have the potential to damage trees, powerlines and unsecure structures and can make driving difficult for large vehicles, campervans and motorcycles," MetService said.