Flooding and slips are likely in the wake of heavy rain forecast for Westland, Canterbury and Nelson, MetService says.
The forecaster warns up to 500mm of rain could fall in the Westland Ranges today and into Thursday.
Up to 250mm is forecast for other parts of Westland and Fiordland, as well as the Canterbury and Otago headwaters, and the northwest Nelson ranges.
MetService said spillover into Canterbury and Otago rivers was expected.
In addition, severe north-west gales are forecast for the Canterbury High Country tomorrow with wind gusts up to 130 kilometres an hour.
A weather watch is in place for Wellington, Wairarapa and Taranaki for tomorrow.