The weather bureau has warned 10 million Australians will be slammed with heavy rain as a severe weather warning is expanded to include almost every state and territory.
It comes as the Australian Defence Force joins the emergency effort in NSW, which is facing its worst flooding conditions in decades.
By Tuesday morning, the NSW State Emergency Service had performed 870 flood rescues and responded to 9700 calls for help.
Residents will have limited time to make it to higher ground as floodwaters are expected to rise rapidly on Tuesday, making it “too dangerous” for a rescue.
“We are moving closer and closer to the inevitable fatality,” NSW Emergency Services Minister David Elliott warned.
While the extreme weather pummelling Sydney and the Mid-North Coast is “far from over”, according to the Bureau of Meteorology (BOM), the warning is no longer contained to NSW.
The BOM warned 10 million Australians were expected to be hit with heavy rain by Tuesday evening as two major weather systems collide.
A tropical rain band is predicted to move in from the west and collide with a trough sitting along the east coast.
This has prompted a heavy rain warning for every state and territory except Western Australia.
“We’ve had days of torrential rain and now this tropical system coming through,” BOM senior meteorologist Jonathan How said.
“It’s a collision of two masses to create a huge rain/thunderstorm band.”
The wet weather for a “huge part of Australia” is forecast to continue until Thursday when the tropical cloud band will have completely pushed the coastal trough off into the Tasman Sea, Mr How said.
NSW is ‘not through the worst of it’
Back in NSW, major flooding is occurring along the Hawkesbury, Nepean and Colo Rivers.
“So pretty treacherous conditions right along the coast,” Mr How said.
Evacuation warnings have been issued for residents northwest of Sydney, including for low-lying properties in North Richmond and Agnes Banks.
The BOM has also issued a warning for moderate flooding along the Nepean River at Penrith with further rises possible.
Floodwaters are also expected to affect the Upper Nepean River at Menangle Bridge.
It’s not just water rescuers have to worry about.
A Fire and Rescue NSW crew were on a mission to save a family of two adults and four young children stranded at a house isolated by floodwater near Port Macquarie when they were faced with the task of removing snakes that “jumped into the life raft” mid-journey.
That occurred during what was just one of the hundreds of rescues that have been made across NSW this week.
More than 18,000 people have evacuated so far.
NSW’s top forecaster Justin Robinson said the record-breaking floods in many of the state’s towns were the worst he’s seen.
“I’ve been a flood forecaster in the bureau for 20 years and this is probably the worst flooding that I’ve experienced and I’ve had to forecast,” Mr Robinson said.
The NSW south coast will get some of the heaviest falls on Tuesday.
The bureau is predicting widespread falls of between 100-200 millimetres across the region and 300 millimetres in some parts.
That means Sydney and the Mid-North Coast could cop another 100 millimetres in the next day or so, and a season’s worth of rain is possible in the west of the state.
“We need to brace ourselves,” Premier Gladys Berejiklian said.
The weather bureau is warning of potentially life-threatening conditions from torrential rain and storms in southern Queensland.
Inland communities braced for flash flooding included Warwick, Toowoomba, Dalby, Roma, Charleville, Birdsville, Emerald, Stanthorpe and Goondiwindi.
The Gold Coast, Brisbane, and the Sunshine Coast have been on high alert, along with Channel Country communities as far west as Birdsville.
Parts of the Gold Coast recorded falls in excess of 200 millimetres to 9am on Monday, including 263 millimetres at North Tambourine, in the Gold Coast hinterland.
Brisbane city and surrounding suburbs also saw widespread falls of 100 millimetres. Beachmere, north of Brisbane, recorded 208 millimetres.
“Minor to moderate flooding across rivers and creeks is likely over the next few days with isolated areas of major flooding possible,” the Bureau of Meteorology warned on Monday afternoon.
“The situation is likely to pose a serious risk to already affected and flooded areas. In some areas, the situation may become life-threatening,” the bureau has warned.
Rescue crews have been forced to stage at least six swift water rescues, four involving people trapped in cars.
One man was plucked from a tree in the southeast after having to abandon his car in floodwaters.
“There’s been inundation to homes, roof damage, trees down. Some of those calls involved multiple problems – water through the roof, coming up through the floor,” SES Queensland state co-ordinator Brian Cox has told AAP.
“We’re nervous because there’s more severe weather predicted, and with the landscape already saturated it means we’re twice as likely to see more flash flooding.”