Emergency services have carried out floodwater rescues across NSW and Queensland, Sydney's main dam is overflowing and a town is under evacuation orders amid rising floodwaters in both states.
The Bureau of Meteorology is carefully watching catchments as far south as Victoria after days of drenching rain across eastern Australia.
People in two cars had lucky escapes when a bridge they were driving over collapsed in floodwaters in New South Wales.
A ute fell into the water as the Nyrang Creek Bridge, between Canowindra and Eugowra in the state's central west, gave way.
The passenger, a 30-year-old man, climbed out the car window, before pulling the female driver to safety.
She was taken to Orange Hospital in a stable condition while the man did not need to go.
A second car following the ute had no time to stop and was forced to jump the collapsing bridge.
The ABC understands a baby and a four-year-old were in the car but all passengers are fine.
Canowindra local Adrian Wheeler says he's never seen the water so high.
"I actually drove through here yesterday when the water was over the road, so I was probably lucky that's not my car there," he said.
"Too much water, too much volume and it's running too fast."
Elsewhere, NSW police rescued four people from floodwaters.
A four-wheel-drive was swept 200 metres downstream from a causeway at Burrell Creek, south-west of Taree, on the state's mid-north coast.
Two men entered the floodwaters to try to help the trapped driver, a 65-year-old man, but also became stranded.
Police threw a rope to the three men and pulled them to safety.
At Muswellbrook in the NSW Upper Hunter, a vehicle that had tried to cross a spillway was swept into floodwaters and found 400m downstream.
Police say the driver, a 52-year-old man, climbed out of the ute but began drifting downstream with the vehicle.
Two police officers waded in to help the man and he was safely returned to shore.
Flash flooding hits southern Queensland
In southern Queensland, nine people were rescued overnight in flash flooding after a band of severe storms dumped a month's worth of rain onto parts of the region.
The Logan River at Rathdowney rose by 10 metres from major flooding, while a major flood warning has been issued for the Logan River at Beaudesert.
In Queensland's South Burnett, a swift water rescue crew launched a boat at Tingoora near Wondai after two cars became stuck in floodwaters.
Two people were rescued from each vehicle, and a dog was also retrieved.
In the Scenic Rim, Queensland Fire and Emergency Services brought in an excavator just before midnight to help get to two campers stuck in rising waters at Barney View.
The heaviest recorded rainfalls overnight were in South-East Queensland, with a number of locations west of Brisbane receiving more than 100mm.
Heavy rainfall wasn't just confined to South-East Queensland, with 50-90mm recorded along the coast of New South Wales as well.
On watch for major flooding
The Bureau of Meteorology (BOM) is watching a number of catchments across southern Queensland, New South Wales and eastern Victoria.
Senior meteorologist Sarah Scully said, in NSW, a warning issued for the Hunter River at Muswellbrook, Denman, Singleton, and Maitland has been upgraded, with major flooding expected on Saturday night.
In the NSW central west, warnings have been issued for the Lachlan River with major flooding expected at Jemalong and moderate flooding at Namami and Condobolin.
Major flooding is also expected at Mandagery Creek at Eugowra on Saturday afternoon, while moderate flooding is occurring along the Belubula River at Canowindra.
With soils across most of eastern Australia near saturation and dams at capacity, any further rainfall risks exacerbating already swollen rivers.
Warragamba Dam spills
Sydney's main water catchment, Warragamba Dam, is overflowing after reaching capacity about 9pm Friday.
"Projections hold steady around at an estimated peak rate of 60-80 gigalitres per day," WaterNSW spokesperson Tony Webber said.
"We expect some impacts in the river downstream."
With another 5-10 millimetres expected to fall on Greater Sydney, there is potential for minor flooding on the Hawkesbury-Nepean Valley at North Richmond and Colo.
Residents are advised any flooding would be well below the flood levels experienced in March this year.
Burrendong Dam received huge inflows on Friday which pushed storage capacity to almost fill the dam's 500GL flood mitigation zone.
Water released overnight caused minor flooding on the lower Macquarie River at Dubbo and Wellington on Saturday morning.
Burrendong is one of the largest inland dams, holding enough water to fill Sydney Harbour three times.
Residents inspect damage
The clean up in flood-affected Scone in the Upper Hunter is underway after major flooding hit the town on Friday, inundating properties.
Resident Ernie Trew said the water rose from the his back fence into the garage within an hour, causing "a few thousand dollars'' worth of damage to work equipment.
In the rush to move possessions to higher ground, his wife slipped on stairs and fractured her ankle.
"We had to get her into the lounge room, the paramedics fixed her leg in there for a while then … got her out on the stretcher," he said.
"[We] then passed her down the steps, loaded her into the dinghy and took her across to the ambulance."
Preparations are also underway in Singleton ahead of possible major flooding tonight.
The State Emergency Service is doorknocking low-lying homes after an evacuation warning was issued.
Sandbags are being distributed from the council building.
The NSW SES is warning people to remain alert to changing conditions, with fresh flood warnings now issued for several communities.
NSW SES spokesperson, Adam Jones has asked people to remain vigilant after 17 flood rescues on Friday.
"Those 17 [on Friday] were too many but as a whole … we're really seeing a [positive] trend and we want to thank those [people]."
