A spokesman for SA Power Networks told InDaily the outage was caused “upstream” by a loss of power at the Heywood inter-connector, in south-west Victoria, which triggered protection equipment at SA power stations  to automatically shutdown.

“It was pretty widespread,” he said.

He dismissed earlier reports that the black out was caused by a shutdown, or load shedding, directed by the state regulator.

Planned work, he said, was being carried out on the network by energy supplier Electranet but he could not confirm if it was responsible for Sunday night’s black out.

“Something unforeseen has clearly happened.”

He said the last time SA blacked out in similar circumstances was in 2004 when 400,000 of the state’s 845,000 customers lost power.

The shutdown  coincided with wild storms which swept across Victoria and New South Wales overnight, leaving a trail of destruction.

While Adelaide’s CBD remained unaffected, homes and properties from Sellicks Beach to Nurioopta, the Barossa Valley, Angaston, to Elizabeth, further north to Munno Para West and east to Belair lost power about 10.30pm until it was restored about midnight.

News of the blackout started appearing on social media after 10.45pm, with suggestions Adelaide may be in for a baby boom mid next year.

July baby boom for #Adelaide then? #blackout

— Rebecca Morse (@RebeccaMorse107) November 1, 2015

Driverless Cars.. Foodless Food Trucks… And Powerless People. Welcome to #Adelaide

— Michael Smyth (@MichaelSmyth_) November 1, 2015

The State Emergency Service received about 100 calls for help.

In Victoria, powerful winds ripped off four roofs and damaged four more near the NSW border, sparking 70 calls for help.

ElectraNet said in a statement it was investigating the “unexpected” interruption.

– with AAP