Thunderstorms and heavy rain have lashed the South Island overnight, causing flooding in Southland.
In Franz Josef, 62 millimetres of rain fell in 12 hours.
State Highway 96 between Mataura and Winton is flooded and has a 30km/h speed restriction in place.
State Highway 94 between Gore and Lumsden and State Highway 6 between Lumsden and Winton have surface flooding.
In Lumsden, 44.8mm of rain fell in 12 hours.
In Otago, State Highway 1 between Balclutha and Gore has a temporary speed restriction of 70km/h.
A shoulder is closed along State Highway 8 between Lawrence and Waitahuna after a slip near the Bloy Road intersection.
The Clutha District Council says up to 30mm of rain has been recorded in the district overnight.
Meanwhile, an alert for dangerous avalanche conditions has been issued for Aoraki Mt Cook National Park this morning.
MetService metereologist Andrew James said the West Coast and now the lower North Island were experiencing thunderstorms.
In Hokitika, 40mm of rain fell overnight.
Mr James said the rain was falling on already-sodden ground after heavy rain in the last few weeks.
More rain is expected with a heavy rain warning in place for Westland, Buller and Southland.
Strong wind gusts possibly reaching 120km/h in open areas of Wairarapa, Wellington, and Marlborough Sounds could damage trees and powerlines, MetService said.
MetService said driving may also be hazardous, especially for high-sided vehicles and motorcycles.