All of South Australia could be without power until the early hours of tomorrow morning after a network failure.
Paul Roberts from SA Power Networks said the authority was investigating the issue.
"We're obviously still trying to find … out [what happened] but what has happened is that the whole state has been blacked out," he said.
"That's due to some upstream issue with the transmission network, we're not receiving any supply through the transmission network.
"We believe — and this is only early information — that there may have been some issue with the interconnector but the state's power system is shut down I think possibly as a protection.
"It means we're not receiving any electricity supply from generators to be able to supply to generators."
Premier Jay Weatherill tweeted about the outrage and said it maybe "for an extended period".
SA Police said just after 4:00pm most intersections in Adelaide were without traffic lights and urged drivers to drive carefully ahead of peak hour.
Adelaide Metro said trains along the Seaford and Tonsley lines and the Glenelg tramline are currently not operating, due to the power outage.
Jenny Scott from the State Library in Adelaide said the building had been evacuated due to the blackout.
"It was just a total power failure across the whole building so of course for safety reasons we had to evacuate.
"It gets quite dark and we worry about customers and staff tripping over things of course and damaging themselves."
Storms and strong winds have lashed South Australia throughout the day with the Bureau of Meteorology issuing severe thunderstorm warning for destructive wind gusts and rain.
The warning said winds of 140kph could occur in Whyalla, Clare, Maitland, Hawker and Leigh Creek, while winds of 90-100kph are forecast for Adelaide and Mount Lofty Ranges.
The SES has tweeted and asked people to stay at home.