The Bureau of Meteorology issued flood warnings while the SES ordered the urgent evacuation of tens of thousands of people in Sydney on Tuesday.
The New South Wales premier, Dominic Perrottet, called for residents to follow those orders as the national death toll for the flood crisis rose to 21.
Driving in many parts of Sydney became unsafe as the deluge hit urban streets and motorways.
An evacuation warning was issued for 800 homes and 2,000 people in low-lying areas below Manly Dam as it began to spill on Tuesday afternoon.
Car parks became rivers and people watched as schools and restaurants were inundated by murky flood waters.
Some took to paddleboards as canals gushed with torrents of brown water.
