MetService is warning of period of heavy rain for the South Island's West Coast through to Saturday afternoon and is forecasting severe gales in some eastern regions of the country.
The heaviest rainfall is expected about the ranges of Westland, where up to 250mm could fall during this time.
Significant spillover is likely into the headwaters of the Otago and Canterbury lakes and rivers, including the hydro lakes.
A period of heavy rain is also forecast over the central North Island on Saturday, particularly in hills and ranges from Taranaki across to the Central Plateau, including Waitomo, Taumarunui, Taupo and the headwaters of the Whanganui River.
Severe gales are forecast for some regions from late Friday through to Saturday morning.
Gusts of up to 120kmh are likely in inland parts of Canterbury, eastern Marlborough, the Marlborough Sounds, Wellington and Wairarapa, with 140kmh gusts possible on exposed hill tops in Wellington.
Flooding in Nelson
Homes and garages in Nelson have been flooded and streets closed following heavy rain in the city. Up to 75mm of rain fell, most of it between 7am and 9am on Friday.
Nelson City Council received about 80 calls from householders, and fire crews have been pumping out floodwater from low-lying garages and homes. The council says the sheer volume of water popped road manhole covers.
The Nelson Fire Service says much of the flooding was caused by blocked drains.
Rocks Road, the main road into Nelson from the south, remains closed to all but heavy vehicles due to a massive slip.
Washington Road was one of the worst hit areas, with rain flooding several garages.
Resident June James said water was about 40cm deep in her garage, and was also in an adjacent lounge room.
A man had to be rescued from his roof, when he slipped and hurt his back after apparently trying to clear a gutter.