An entire Australian state has lost power as a strong storm lashes the region with heavy rain and fierce winds.

Most traffic lights were knocked out during Wednesday's storm, causing gridlock across the state that is home to 1.7 million people. Police said they were responding to several reports of people stuck in elevators, and emergency services and hospitals were running on back-up power.

South Australia state Premier Jay Weatherill said it wasn't clear what caused the power outage. Crews were working to restore power, but it was expected to take hours to get everything running again.

The storm was expected to pummel the region through Thursday, with wind gusts exceeding 100 kilometers an hour (60 miles an hour) in places.