Residents in Broome and Derby have been warned their towns are likely to be isolated within 12 hours amid a once-in-a-century flood in Western Australia's Kimberley region.
About 60,000 cubic metres of water per second is flowing down the swollen Fitzroy River, cutting the only major transport route, including a major bridge, to the north of the state and Darwin.
"It's one the highest flow rates we've ever seen in an Australian river," meteorologist James Ashley told reporters on Wednesday.
"The amount of water moving down the Fitzroy River in a day is about what Perth uses water-wise in 20 years."
Fitzroy Crossing and dozens of Indigenous communities have been hit by record flooding, as the torrent snakes its way toward Derby on the WA coast, where the region's major airport at Broome is already closed.
"The Kimberley is experiencing a very unpredictable, rare and severe flood event," Fire and Emergency Services Commissioner Darren Klemm told reporters on Wednesday.
"This is a rapidly evolving emergency situation. Our main priority is preservation of life and safely evacuating people from impacted areas."
Authorities have told people in Broome and Derby to prepare to be cut off by flooding "as early as tomorrow morning" as ex-tropical cyclone Ellie continues to dump heavy rain across the region.
"Broome is experiencing heavy rainfall and strong winds," Mr Klemm said.
"The Bureau of Meteorology is expecting up to and in some cases over 200mm of rain in some locations."
The weather system is hovering east of Broome, where it was forecast to remain throughout Wednesday, before moving slowly east towards the Northern Territory at the weekend.
Two Australian Defence Force C-130 Hercules aircraft that can carry 80 passengers and a C-27 will be deployed to the region from Thursday to join a fleet of rescue helicopters carrying out evacuations and deliveries of urgent supplies.
"However, weather conditions and flooding at airports are creating numerous logistical problems," Mr Klemm said.
Fitzroy Crossing's evacuation centre is at capacity, with a second to be opened as flood rescues continue in the remote town and at outlying Indigenous communities cut off by water.
"We will continue to undertake rescues where possible but people need to understand this will take time," Mr Klemm said.
The bureau warns the Fitzroy River is still rising at the town and likely to peak at 15.8 metres later on Wednesday, smashing records.
The town's supermarket is flooded, along with most roads as people, stock and wildlife clamber for the remaining dry ground.
"People are suffering ... people are scared," WA Emergency Services Minister Stephen Dawson said.
"The weather in Fitzroy is still challenging ... and there is water over the airstrip."
Flooding is also likely downstream at Noonkanbah, Willare, Fitzroy Barrage and Looma.
Mr Dawson said pastoralists and livestock had also been impacted significantly by the flooding.
"Until the floodwaters start to recede it won't be possible to undertake a full assessment of damage and stock losses in the region," he said.
"This is very distressing for the community."
Mr Dawson said authorities were working on a plan to transport food and other supplies to the north of the state after the flooding subsides.
He said WA's biosecurity rules and the flood-damaged Fitzroy Bridge, which "hasn't collapsed yet", could necessitate an ongoing airlift to brings goods from the south.
Prime Minister Anthony Albanese tweeted a message of support to flood victims across the country on Wednesday.
"My thoughts are with all those families dealing with floodwaters today - from the Kimberley to Menindee to the SA Riverlands," Mr Albanese tweeted.
"We're working with state and local governments to help in whatever way we can."
Major flooding continues in the western NSW town of Menindee, where the Darling River was holding steady at around 10.2m on Wednesday but could rise to 10.7m from Thursday, above the 1976 flood record of 10.47m.