Rain-swollen rivers spilled mud-brown waters across swathes of Sydney on Tuesday, swamping homes and roads while forcing thousands to flee.
Emergency services have now instructed about 50,000 people to evacuate or to prepare to escape the rising waters in New South Wales, officials said.
Emergency workers carried out 22 flood rescues in Sydney overnight, they said, with the support of 100 army troops deployed to the state.
The floods, heavy rain and powerful winds led to power cuts for 19,000 homes, officials said.
Australia has been at the sharp end of climate change, with droughts, deadly bushfires, bleaching events on the Great Barrier Reef and floods becoming more common and intense as global weather patterns change.
Higher temperatures mean the atmosphere holds more moisture, unleashing more rain.
“Sydney is not out of danger, this is not a time to be complacent,” State Emergency Services commissioner Carlene York told a news conference.
“It’s risky out there.”
Meteorologists predicted the weather front would move northwards along the east coast after dumping rain on Sydney for four days.
The federal government has declared a natural disaster in 23 flooded parts of New South Wales, unlocking relief payments to stricken residents.
