MetService advises motorists to heed warnings of heavy rain and gale force winds as a band of bad weather passes over most of the country.
Torrential rain fell in Westland and Fiordland on Monday and in Otago and Canterbury overnight.
There are high winds and rain over the upper South Island and much of the North Island.
MetService says 500mm of rain is due for the Southern Alps and the Rangitata, Waimakariri, and Rakaia rivers are expected to swell.
The Waitaki and Clutha rivers are also expected to rise.
Duty forecaster Oliver Druce says Wellington will have gusts up to 160km per hour as winds sweep the east coast from North Canterbury to Gisborne.
Police say some power lines are down in Wellington, in the suburbs of Rongotai and Khandallah.
Wind gusts of up to 160km per hour in Wellington are causing disruption to flights in and out of the capital.
So far on Tuesday, two inward flights have been cancelled and five delayed. One departure has been cancelled and four others delayed.
Police say a slip has covered the road on the Crown Range Road between Wanaka and the Gibbston Valley.
Earth moving equipment is on its way. Contractors say it will take most of the day to clear.
In Marlborough, a tree is blocking the northbound lane of State Highway Six, about 5km north of Havelock.
Another tree has fallen down, blocking the southbound lane of State Highway 60, around 30km south of Motueka.
In Westland, on State Highway Six, on Haast Highway, Jacob's River bridge is closed due to flooding.