Severe weather has cut power to all of South Australia.
SA Power Networks says the state currently has no upstream supply through the transmission network.
Police have called on all people to avoid travel if possible, with the blackout causing widespread traffic disruptions, especially in Adelaide.
SA Premier Jay Weatherill said the power outage could continue for an "extended period".
There was no immediate information on the exact cause of the blackout which resulted in gridlock on many of Adelaide's CBD and arterial roads.
Police dispatched patrols to regulate traffic at major intersections.
The blackout came as strong winds and heavy rain lashed parts of SA with the Bureau of Meteorology warning super cell thunderstorms were possible across the central and mid-north districts.
The bureau issued a severe thunderstorm warning for an area stretching from Victor Harbor, south of Adelaide, to Marree.
It said super cells within those storms could produce wind gusts of up to 140km/h along with heavy rain that could cause flash flooding.
The major centres to feel the impact of the storms included Adelaide, Whyalla, Port Augusta, Hawker, Port Pirie, Clare, Roxby Downs and Leigh Creek.
The extreme weather reached the city around midday and was expected to dump up to 100mm of rain in some areas, including the Adelaide Hills, where a flood warning was in place.
Similar falls were possible in the mid-north with the cyclonic conditions expected to whip up large swells along the state's coastal waters, producing 10-metre waves.
By late afternoon the State Emergency Service had responded to more than 270 calls for help, most because of fallen trees or rising water.
It earlier distributed more than 43,000 sandbags to local residents concerned about possible flooding after severe weather just two weeks ago flooded 80 homes across Adelaide and the Mt Lofty Ranges.
The bureau said the wild weather was the result of a front and intense low-pressure system.
It said records suggest such a severe system was last reported across SA more than 50 years ago.
