There has been a brief reprieve from the weekend deluge but heavy rain is expected to lash the western and southern parts of NSW on Wednesday and Thursday.
The heaviest rain is expected to arrive on Thursday, with up to 100mm predicted in some areas.
Seven rivers could experience flooding in the coming days, the Bureau of Meteorology says.
Major inundation is occurring along the Murrumbidgee with the Riverina town of Gundagai on high alert, and flooding is also possible downstream at major regional centre Wagga Wagga.
Evacuation orders are in place in parts of Dubbo, Wagga and the Hawkesbury, north of Sydney.
SES volunteers have responded to more than 1000 calls for help since Friday evening, including 155 in the past 24 hours, and conducted six rescues.
Emergency Services Minister Steph Cooke told NSW parliament on Tuesday that concern for remote communities was high as the "widespread" weather system hits the state on Wednesday
"The SES is concerned about many of our rural, regional and remote communities ... in Nyngan, Warren, Wee Waa, Gunnedah, Moree, Bathurst and Forbes".
But she says emergency personnel are now better prepared than they were before the previous engulfing floods in March.
She noted 1300 extra volunteers have been added to the emergency service, call-taking capacity has been beefed up, a three-tier simple warning system for residents has been put in place and up to 14 night-time helicopters for the state are on stand-by.
Numerous rivers are at major flood levels, particularly in the north and west of the state.
The Murrumbidgee River was at 9.04 metres at Gundagai early on Tuesday, with moderate flooding expected at Wagga in the coming days.
At Forbes, the Lachlan River is likely to peak near 10.40m, just below the major flood level, on Wednesday, bringing major flooding to Cottons Weir and Jemalong.
The Namoi River at Gunnedah peaked at 7.75m on Monday night, with the main flood peak now downstream of Boggabri and expected to reach Narrabri on Wednesday.
Victorians are being urged to enjoy the warm weather while it lasts, with the State Emergency Service and BOM bracing for flooding in the next few days.
"This event is probably the most significant rain event widespread across the state this year, certainly the most significant in recent months," BOM senior meteorologist Kevin Parkin told reporters in Melbourne on Tuesday.
"We've got a short-term flash flood risk as a result of that rainfall intensity and then a longer-term riverine flooding risk," he said.
Watch and act flood warnings have been issued for several rivers across the state, with the SES urging Victorians not to camp near streams and rivers this weekend and avoid driving to northern parts.
In Queensland, minor flood warnings are current for the Bulloo, Lower Macintyre, Paroo, Bokhara and Barcoo rivers, while northern Tasmania is also set to face heavy rain between Wednesday and Friday, with up to 100mm expected in some parts.
The BOM has meanwhile released its severe weather long-range forecast into 2023.
It expects an increased risk of tropical cyclones and tropical lows and widespread flooding for eastern and northern Australia.
While there is "normal bushfire potential" in the eastern states, there will be an elevated risk of grass fires in southern Australia and a higher risk of prolonged heatwaves with higher humidity.
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