Amazing video shot from the air has shown the extent of flooding in Gore as the Mataura River runs at the highest level many locals have seen.
The view from the sky shows hundreds of homes flooded while many farms, fields and roads have been completely drowned from the torrential downpours and floods.
Low-lying residents have been evacuated, bridges and roads closed and Gore has been left isolated.
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Inspector Jon Bisset, speaking from Mataura, said he had never seen the river run so high.
"I grew up in Southland and I've never seen the river like that."
The river was expected to peak at 2450 cumecs at Gore before 9.20am, and at Mataura with 2665 cumecs at 11.50am.
Southland Emergency Management Chair Neville Cook said people should get out immediately.
As well as leaving, people were encouraged to check on their neighbours and to share the information with those who might not have seen the warnings.
Main routes around Gore and Matauara are closed: State Highway 96 Winton to Mataura (between Brown Rd and SH1), SH1 from Mataura to Gore and from to Clinton, SH90 McNab to Tapanui (from SH1 intersection to Station d), SH93 from Clinton to Mataura and SH94 Gore to Mandeville (Waimea Highway).
Hokonui Breakfast radio Luke Howden said they had to wade through waist-high water to leave their house on Ontario St in Gore late yesterday afternoon.
He said they saw the water rise very rapidly about 4pm.
"Before we knew it, it was licking on the back doorstep. We had the fire crews outside whistling for us to grab some things and get out.
"It was a matter of wading through waist-high water to get to the end of the street and into safety."
His partner, Amber Geerlings, said they only had about half an hour to pack a change of clothes, some family photos and grab the dog before getting out.
She said they were waiting to hear when they would be okay to go return to their house and were now dreading what they might find.
"Since the water was at our front door when we left, we'll have to see what it looks like."
The couple had planned to go to singer Sir Elton John's concert before taking a few days off, but were unable to after the bad weather struck.
Anyone who finds themselves in danger or is unable to evacuate from their home is urged to call 111 immediately.
- Additional reporting by ODT