A state of emergency has been declared in Fiordland after flooding cut off the only road out of Milford Sound, leaving more than 380 people stranded.

Photo: NZTA

State Highway 94 between Te Anau and Milford, dotted with slips and flooding, is closed and expected to remain so for several days.

The visitors' carparks and terminal in Milford Sound are flooded and staff are monitoring ponds in the area.

The Transport Agency said the highway - the only road in or out of Milford Sound - would remain closed throughout today and into tomorrow morning.

The next update was not expected before 1pm tomorrow.

Photo: NZTA

Southland Mayor Gary Tong said the state of emergency applies to Milford, Te Anau and Manapouri.

Several vehicles have been spotted on State Highway 94 and emergency services will be flown into the area by helicopter to check on the occupants of vehicles stranded on the road, and tracks and camp sites.

He said the only way out was by sea or air.

Milford Track was cleared during the weekend, but Tong said people may be on other tracks in the area.

In Milford Sound, Mitre Peak Lodge, run by Ultimate Hikes, has been turned in to a Civil Defence centre.

Shaun Liddy from Ultimate Hikes said it was a large building and other tour companies were helping out with food and other resourcing.

Emergency Management Southland controller Angus McKay said the 382 people in Milford Sound, including staff and visitors, were either in Mitre Peak Lodge or on the tourist boats.

"They have plenty of food and are safe and warm," he said.

"The Cleddau River and high tides had caused flooding this morning and staff were monitoring the expected rainfall and tides throughout today and tomorrow, when more heavy rain is expected in the early morning.

"No one is on the Milford Track as it was cleared at the weekend.

"Milford Road is likely to be closed for some days because of slips and flooding damage. Milford Road Alliance staff are checking the road for vehicles."

UPDATE: 9:00 AM

SH94 Milford Rd is expected to remain CLOSED until Tuesday as heavy rain is not expected to ease, An update is expected at 1 pm. ^JPhttps://t.co/3e7GuGJNGd pic.twitter.com/zMoydncBQb — NZTA Otago/Southland (@NZTAOS) February 2, 2020

The Invercargill emergency centre has been activated.

Weather warning for Otago and Southland

MetService issued a heavy rain warning for the area with a further 100 to 250mm of rain forecast to fall on top of what had already fallen.

Photo: Facebook / Civil Defence Southland

There are warnings and watches for heavy rain across much of Otago and Southland, but the area expected to be most affected is Westland and Fiordland south of Hokitka where the MetService has upgraded the warning level to a "red warning" from orange.

SH94 was closed earlier today between Cascade Creek and West Gate (the Chasm).

NZTA journey manager Peter Brown said a small number of tourists were taken by helicopter out from Forks Bridge about 1.5km from the Homer Tunnel.

A bus load of 27 people were expected to be airlifted out at Hollyford Rd ''in the next hour or so''.

''There is extensive damage from Lake Gunn to the Homer Tunnel which will delay us opening this road quickly and there is still a section we haven't inspected due to bad weather preventing a fly-over.''

The Milford Road Alliance said flooding was causing "significant damage" with rainfall rates of 55mm an hour.

The alliance was checking the road for vehicles.

MetService said the event had high potential for "further significant impacts, such as major slips, road closures and flooding, in the next 24 to 36 hours.

A series of fronts was forecast to move east across the South Island from yesterday morning through into tomorrow afternoon, bringing periods of heavy rain to the west and the south of the South Island and strong west-to-northwest winds to parts of southern and central New Zealand.

SOUTH ISLAND SEVERE WEATHER WARNINGS & WATCHES IN PLACE

A number of Heavy Rain Warnings are in place for the West Coast, Otago & Southland. As well as a Strong Wind Watch in place for Otago, Canterbury & Marlborough. Take care & plan your journey^SM https://t.co/uRRkfF665e pic.twitter.com/zXJwxHvYmy — NZTA Canterbury/WC (@NZTACWC) February 2, 2020

A MetService spokesman said a a heavy rain warning is in force for Fiordland, Westland, the headwaters of Otago Lakes and Rivers, Southland and Clutha.

The heavy rain watch for Central Otago, the Southern Lakes and the headwaters of the Canterbury lakes and rivers have now been upgraded to an orange warning. Watches for heavy rain have now been issued for Dunedin and Buller.

"Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous."

In the headwaters of the Otago lakes and rivers, up to 450mm of rain is expected to accumulate near the main divide, and up to 280mm is expected within 15km east of the divide until 1pm tomorrow.

Flooding has also closed the Glenorchy-Paradise Road. The Queenstown Lakes District Council said the Routeburn Road was also closed on the Glenorchy side of the the Dart River, also due to flooding.

West Coast

The highway between Fox Glacier township and Haast in South Westland reopened this morning after rain washed out a culvert at Thirsty Culvert late yesterday.

A Transport Agency spokesperson said SH6 was closed shortly after 5pm yesterday but reopened at 9.30am today.

In Westland (from Harihari southwards), up to 500mm of rain may accumulate about the ranges, and up to 160mm near the coast until 2pm tomorrow.

Peak rates throughout these regions were generally expected to be up to 25mm an hour and up to 35mm to 40mm if there were thunderstorms, he said.

There is also a strong wind watch in place for eastern parts of southern and central New Zealand.

- with additional reporting by Otago Daily Times