Evacuations are going to plan in the Gore District where river levels have started to peak after intense rain.
South Gore and Balclutha are becoming inundated and power is being cut to flood zones for safety.
A video of some of that inundation, shared to Facebook by local National MP Hamish Walker on Wednesday morning, shows the extent of the devastating flooding in the area.
Residents in low-lying areas of Gore, Wyndham and Mataura were earlier told they needed to evacuate immediately as river levels continue to rise.
The river is set to peak at Mataura by midday.
Emergency Management Southland is urging people not to be complacent with people told they need to evacuate immediately.
Civil Defence says people should call 111 if they are in danger.
