Thousands of Australians were ordered to evacuate their homes in Sydney's northwest and elsewhere in New South Wales state as heavy rainfall flooded rivers and waterways.
State Emergency Service Commissioner Murray Kear on Saturday said that 3,500 people were subject to evacuation orders as 75 percent of the state was affected by flooding.
The swollen Hawkesbury-Nepean was threatening areas on Sydney's semi-rural northwestern outskirts near the town of Richmond, with several towns, caravan parks and low-lying homes evacuated.
"This is a moderate flood but it's unusual because we haven't seen water in this river system in a while," Kear said of the waters, which have swamped bridges and closed roads.
Days of heavy rain after a damp summer have seen Sydney's Warragamba Dam, the main source of the city's drinking water, reach capacity for the first time in 14 years -- causing the water to flow over its spillways Friday.
Authorities said the rainband stretching across the southern half of New South Wales has produced up to 200 millimetres (eight inches) of rain over a three-day period and the downpour would continue over the weekend.
Kear said people needed to be prepared for flash flooding, with the prospect of a further 200 millimetres of rain over the next two days.
"This could lead to homes being isolated or inundated by water," he said.
Across New South Wales, some 2,300 people had been cut off by the surging torrents and more than 1,500 evacuated from areas south of Sydney and from towns near the national capital Canberra due to rising flood levels.
Kear said no homes had been inundated in the past 24 hours, but he said there had been more than 40 flood rescues -- including saving people trapped in cars -- and warned people against attempting to drive through floodwaters.
Meanwhile the southern state of Victoria was also bracing for continued heavy rainfall and more flooding, with several northern towns isolated by the rising waters.
"This extra rain coming, it will be really setting in there this afternoon, continuing overnight and then clearing out tomorrow," the Bureau of Meteorology's Phil King told the ABC.