MetService has issued its first-ever 'red warning' as an onslaught of heavy rain slams into the South Island, trapping over 380 people at Milford Sound.
This warning is reserved for the "most extreme weather events" where "significant impact and disruption" is expected - and MetService warns people need to "act now".
The red warning has been issued for Westland south of Hokitika and Fiordland north of George Sound as rain pummels the region.
There has been 350mm of rain in the past 24 hours at Milford Sound, and MetService expects a further 300-450mm of rain in parts of Fiordland and Westland by Tuesday afternoon.
"This red warning is issued after consultation with the West Coast Regional Council and the local Civil Defence after careful consideration of the impacts the area could see in this kind of weather event," says MetService meteorologist and head of weather communication, Lisa Murray.
"This amount of rain can cause significant impacts to those living or travelling through the area. You can expect dangerous river conditions, significant flooding, and slips. It is likely to disrupt travel, making some roads impassable and possibly isolating communities."
A state of emergency has been declared in Fiordland after State Highway 94, between Te Anau and Milford, was cut due to heavy flooding.
Over 300 people have been trapped at Milford Sound as a result.
Emergency Management Southland controller Angus McKay says the 382 people in the Milford area are made up of staff and visitors and are either in Mitre Peak Lodge or on the tourist boats. They have plenty of food and are safe and warm.
The NZTA says the highway will remain closed throughout today and into Tuesday morning.
The Invercargill emergency centre has been activated.