Severe storms have knocked out power to the entire state of South Australia, home to 1.7 million people, energy authorities say.
The Bureau of Meteorology said a vigorous cold front was moving across the state with an intense low pressure system due on Thursday.
"We'll have gale force winds and large seas (across the south of the country); also heavy rain and thunderstorms, which will lead to renewed river rises," it said on its website.
SA Power Networks said repairs to its transmission network were underway.
"There were more than 21,000 lightning strikes recorded over a 12-hour period from midday yesterday on the West Coast, and as a result it is likely some damage has occurred to our distribution network," it said.
The state has been brought to a standstill, with ports closed, trains and trams stopped, traffic lights out and long commuter delays, state agencies said.
South Australia was relying on accessing power from Australia's populous east coast via a power interconnector with the neighbouring state of Victoria when there was a failure on Wednesday.
No power was flowing from Victoria into South Australia, said a spokesman for the Australian Energy Market Operator, which operates the power systems in southern and eastern Australia.
When the state tried to compensate, it experienced what is known as a "voltage collapse", Simon Emms, executive manager of network services at network operator ElectraNet, told ABC Radio, due to storm damage to power lines. This led to a statewide outage.
"Now, clearly, questions will be raised," Federal Minister for the Environment and Energy Josh Frydenberg told Sky News.
"Serious questions will be raised that need to be answered as to how this extreme weather event could take out the whole of the electricity supply across a major state such as South Australia."
The impact was wide-ranging, with traffic coming to a standstill in the state capital of Adelaide while power supplies were disrupted to BHP Billiton's Olympic Dam copper-uranium mine, a huge mining operation more than 500km to the northwest.
A BHP spokesman said back-up power generation was being used to run critical infrastructure. - Reuters
Stay at home if you can. Electric trains, trams and traffic lights are down across #Adelaide— SA SES (@SA_SES) September 28, 2016
Main roads and side streets are now flooding. Please give each other extra room and time to pass safely. #AdelaideStorm— RAA (@RAAofSA) September 28, 2016