Emergency Management Southland has declared a state of emergency for the Fiordland Community Board area to provide a coordinated response to the flooding emergency in Milford Sound.

A statement released this afternoon said the state of emergency would allow agencies in their response to gather "resources for the remote area."

Emergency Management Southland controller Angus McKay said Southland District Council Mayor Gary Tong signed off on the declaration at 1.40pm this afternoon. 

"Everyone in the Milford township is accounted for and will be staying in Milford Sound for at least the next day because of flooding in the sound and along Milford Road." 

Mr McKay said the 382 people were made up of staff and visitors are and are either in Mitre Peak Lodge or on the tourist boats.

He said they have plenty of food and are safe and warm. 

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. 

Staff are also monitoring the wastewater ponds at the sound, with the visitors’ car parks and the visitor terminal currently flooded.  

Mr McKay said nobody was on the Milford Track as it was cleared at the weekend. 

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

The NZTA said major damage had occured between the divide and tunnel at multiple sites on Milford Road and the road was expected to remain closed for the remainder of this week with daily updates provided.

It said the Hollyford Road had also been damaged to Gunns Camp and would be closed Tuesday as well.

The Invercargill emergency centre has been activated to monitor and respond if needed Mr McKay said.

A heavy rain remains in place for Fiordland, north of George sound, with expected falls of up to 450mm along the ranges and up to 150mm near the cost expected till 4pm tomorrow afternoon. 

The MetService alert warned the weather would cause dangerous river conditions and significant flooding, with slips and floodwaters likely to disrupt travel and making some roads impassable and possibly isolating communities.

Peak rates rain would be around 15 to 25mm/h but could increase to 25 to 40mm/h, mostly with thunderstorms the alert said.

Flooding has also impacted other parts of the region, with SH94 in Croydon near the intersection with Kingdon Road and SH93 in Clinton near the intersection with Three Stones Road both under a 30km/h speed restriction due to surface flooding.

The wild weather also continues to cause power issues for people across Southland, with several customers experiencing "power interruptions and network disturbances" PowerNet chief executive Jason Franklin said.