Severe thunderstorms, large hail, damaging winds and heavy rain are forecast for parts of Victoria and NSW marking a wet and stormy start to the week.
The fierce weather follows days of heavy rain in northern Queensland where coastal and inland centres including Townsville, Cardwell and Ingham were most affected.
Flood-hit communities have been urged to keep up to date with the latest warnings, with fears of more rain on the way.
The Bureau of Meteorology forecasts severe thunderstorms from Dubbo all the way to Wagga Wagga and Albury-Wodonga on the NSW-Victoria border.
Senior meteorologist Dean Narramore said the wild weather was expected from Sunday afternoon.
"We could see severe thunderstorms with large hails, damaging winds and heavy rainfall and that could lead to flash flooding of businesses, roads and property," he said on Sunday.
"We could also see dangerous driving conditions with these storms, as well as damage to homes, properties and businesses, with trees and power lines down, particularly with those damaging winds."
Even bigger storms were expected on Monday through much of inland NSW and northeast Victoria.
"We could see widespread falls of 25 to 50mm through eastern Victoria and much of central and eastern NSW," Mr Narramore said.
"And we could see even heavier falls in excess of 100mm possible through parts of eastern Victoria and particularly around central and south eastern parts of NSW."
In Queensland, major flood warnings are in place for the Herbert, Burdekin, Haughton, Flinders, Cape and the Western Rivers, with minor-to-moderate warnings for a number of other catchments through northeast and northern inland regions.
Senior meteorologist Myriam Bradbury said 24-hour rainfall totals could reach 250mm.
"This rain is falling onto saturated land, meaning it will quickly run off and top up already swollen rivers," she said.
"This means that even moderate rainfall totals could cause swift river rises and could lead to dangerous flooding conditions."
The flood warnings come as communities in Western Australia's north remain on watch for a possible tropical cyclone.
The bureau said the tropical low near the north Kimberley coast could become a cyclone on Monday.
On Sunday morning it was situated 380km from Broome and 160km northwest of Kuri Bay.
"The low is forecast to move southwest off the Kimberley coast and develop, potentially reaching cyclone intensity on Monday," the bureau said.
Wind gusts of up to 100km/h were possible along the coast between Cockatoo Island and Beagle Bay by Monday afternoon, possibly extending further towards Broome and Bidyadanga.
Heavy rain was also possible between Cockatoo Island and Broome from Sunday.
Flooding in Queensland in the past week forced hundreds of people to evacuate their homes and left communities without power.
A major bridge in the town of Ingham was washed away, with the Australian Defence Force called in to restore temporary access for crucial supplies.
Some residents have started to return to flood-ravaged homes, with more than 4000 storm and flood-related insurance claims so far.
The total damage bill is unknown.
So far $8 million is available for affected residents through the Commonwealth's community relief fund while Queensland Premier David Crisafulli is pushing for federal support to lift bridges above flood level along the Bruce Highway.
Queensland Reconstruction Authority chief executive Jake Ellwood warned the clean-up would be hard, with an enormous toll on the mental health of affected people expected in addition to physical and economic impacts.
"Recovery and reconstruction is not a days and weeks event - it is months and years," the retired Major General told reporters in Townsville on Saturday.
