A landslide has hit a hut on the Routeburn Track in Fiordland with 31 people inside as torrential rain battered Fiordland overnight.

The slip hit the Howden Hut at 1.30am, and all those inside are safe and awaiting evacuation.

Emergency Management Southland controller Angus McKay said the priority was to get them out this morning, along with trampers at other huts.

The Howden Hut on the Routeburn Track

It was not known how many people were in the other huts, he said, but emergency management was working with helicopter pilots to evacuate them.

A state of emergency was declared in the area yesterday afternoon as heavy rain and slips closed State Highway 94, the only road into Milford Sound.

Some tourists were flown out yesterday, and the remaining 195 tourists in Milford Sound may be stuck there for another day.

The tourists are in three lodges in the Milford Sound area, where 200 hotel and lodge staff are also stranded.

The only way out is by air and sea and evacuations will depend on weather conditions.

McKay said safety was the priority, and with more heavy rain forecast the tourists could be stuck for another night.

Milford Sound had 350mm of rain in the 24 hours to 10am yesterday, and MetService had forecast a further 250mm-350mm of rain on the ranges by this afternoon. On the coast the rain was expected to ease.

MetService issued a Red warning for Westland south of Hokitika and Fiordland north of George Sound.