An attempt to rescue dozens of motorists stuck in Fox Glacier will get underway on Friday morning.
Extreme weather from ex-tropical cyclone Fehi has trapped nearly 100 people in vehicles between Ross and Makaroa.
Fox Glacier, Franz Josef, Whataroa, and Haast have all been cut off by slips.
- Fehi wreaks havoc across New Zealand
- Bystanders bowled over by huge storm surge in Nelson
- Man wiped off bike as he tries to tackle Auckland's flooded Tamaki Drive
Westland's Civil Emergency team says the stranded drivers are not in danger, and all have water and shelter. A helicopter will be flown over them at first light to make sure they're okay.
In Nelson, a storm surge and king tide caused a failure at a sewage pump, resulting in an overflow of untreated sewage and stormwater contaminants into Nelson Haven and Waimea Estuary.
Nelson City Council is advising the public not to swim or have contact with the water in those areas, including Tahunanui Beach.
The storm is also causing trouble in Dunedin, which declared a state of emergency on Thursday, leaving residents with a major clean-up on their hands over the weekend.
The state of emergency was called yesterday afternoon after more than 108mm of rain fell, causing waste water overflows and surface flooding.
Fire and emergency shift manager Riwai Grace says southern crews were called to 210 of the 228 weather-related events across the country on Thursday.
However it's not all bad news - the wet weather has brought much needed relief to Otago farmers.
A drought was declared across the region just a few days ago as temperatures rose to the late 30s in most parts.
Federated Farmers' Otago president Phill Hunt told Newshub they've been desperate for a good soaking.
"The problem that we've had is not only through lack of grass but also through lack of stockwater.
"This rain will have significantly filled them up."
Mr Hunt says people should still check on their rural neighbours, as it will take time for the rain to make a huge impact.
A state of emergency was also declared in Buller, however Civil Defence emergency management officer Erica Andrews says conditions seem to be improving.
"The tide at 12:45am this morning didn't appear to be as severe as the one that was at lunchtime [on Thursday]."
Emergency services are monitoring the situation and more updates are to come. Heavy rain will continue for parts of the South Island on Friday.