Power slowly returns to storm-hit South Australia

Adelaide was plunged into darkness overnight (AAP)
Adelaide was plunged into darkness overnight (AAP)

South Australia authorities are warning residents there will likely be further outages as a severe storm rages across the state.

The entire state of South Australia was without power on Wednesday night. The weather front brought with it more than 130,000 lightning strikes, causing traffic chaos and outages to 1.7 million people.

South Australia Power Network is warning customers to prepare for "extended outages" as the wild weather continues.

South Australia state police commissioner Grant Stevens told residents to stay inside after the power went out just before 4pm Wednesday (local time). Water pumping stations also went offline.

Power has been restored to much of the Adelaide metropolitan area and the northern parts of the state, but the Eyre Peninsula to the west is expected to be without services into Thursday.

Questions are now being raised about how a storm could wipe out power to an entire state.

The worst may be yet to come, with a third storm system bearing down on the state - though it's expected to pass by capital Adelaide.

Terry Dwyer of the State Emergency Service says residents need to brace themselves.

"There's some high winds coming through again, there's a second front coming through and we're going to get a further 10mm of rainfall," he told Newshub.

"Then around about the middle of the day it'll intensify again, and we're expecting some thunderstorms."

They've responded to almost 500 emergency calls so far.