Sydney has been deluged by the heaviest November rain it has experienced in decades, causing flash-flooding, traffic chaos and power cuts.
Heavy rain fell throughout Wednesday, the city at one point receiving its average monthly rainfall in two hours.
Officials said dozens of vehicles crashed in the stormy conditions, with winds of up to 90km/h (55mph) also recorded.
At least two deaths have been blamed on the storm.
A 14-year-old boy died in a car accident in Thornleigh, in the north of Sydney on Wednesday morning.
A volunteer with the state's emergency service also died while out on duty, and two police officers were injured after being hit by a falling tree while trying to help Sydney motorists, authorities said.
Images posted online showed downed trees and flooded roads, houses and train stations.
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The weather played havoc with commuters in Australia's biggest city, with many transport services cancelled or delayed - including 130 flights at the international airport.
A spokeswoman for Sydney airport said it was forced to operate only one runway after two others were closed due to the storm.
Australia's Bureau of Meteorology said it was the region's wettest November day since 1984.
"The intensity of that rainfall was phenomenal - 91mm fell in 90 minutes," forecaster Rob Taggart told the Australian Broadcasting Corporation.
The storm centred on coastal parts of New South Wales (NSW), but was reported to have missed many inland regions affected by drought.
Ausgrid, the country's biggest electricity network, said the storm had cut electricity to more than 8,000 customers around the Sydney area.
By Wednesday evening, more than 3,250 homes and businesses were still reported to be without power.
Authorities urged people to try to avoid travelling where possible, as the two main phases of the rain fell around commuting times.
"We cannot stress enough that motorists should never attempt to drive through flood waters or cross flooded causeways," assistant commissioner Michael Corboy of NSW Police said on Wednesday.
The floods are not the only extreme weather currently being experienced in Australia.
In Queensland, further north, thousands have been evacuated as an unprecedented heatwave grips the region, sparking destructive bushfires and dust-storms.