The flood waters peaked in Fitzroy Crossing at a record 15.81m late on Wednesday, with mass evacuations in and around the remote town.
Long-term resident and mechanic Dwayne Ben says the water rose further and faster than any other flood he had seen, catching many people, including himself, by surprise.
"I'm here at my workshop and everything is completely destroyed," he told AAP on Friday.
Mr Ben said the water flooded the business overnight, destroying all the equipment and 12 vehicles, including a police car in for repair.
He said damage in the town of about 1200 people was extensive but it was difficult to tell exactly how many homes and businesses had been destroyed because many roads were still flooded.
"As far as the communities, Muludja and places like that, they'd be completely gone," he said.
"Depending on what happens now the water has gone down further towards Noonkanbah and that, it might be thousands of homes."
Mr Ben said other businesses in the town had also also been inundated by water and damaged, including the town's oldest hotel on the river bank.
"The Crossing Inn, which is a very historic building and pub, it's completely gone, from what I heard," he said.
"At the moment they're cleaning up the supermarket so they can get food back in there ... They only just got power on."
The Bureau of Meteorology said the Fitzroy River's massive flood peak had now moved downstream and slammed into the tiny Indigenous community of Noonkanbah.
Helicopters started plucking anxious residents from the sodden outstation, 280km inland from Broome, on Thursday as about 60,000 cubic metres of water per second flowed down the swollen waterway.
It's expected to create a 50km-wide inland sea as it spreads across the flood plain.
"Downstream of Noonkanbah significant flooding is (also) occurring, however river level data at Fitzroy Barrage and Looma is currently unavailable," the bureau said in a statement.
Flooding is also occurring at Willare, with seven-day rainfall totals up to 600mm recorded across the region.
A 400km section of the Great Northern Highway south of Broome has been closed and a 500km section of the same freight route between Willare and Halls Creek remains closed.
Authorities say it could take weeks, if not months, for the only road transport link to the north of the state to reopen due to road and bridge damage.
The unprecedented flooding has been caused by ex-tropical cyclone Ellie, which on Friday afternoon was about 300km southeast of Broome.
The slow-moving weather system started moving southeast on Friday and is expected to move further inland towards the Northern Territory over the weekend and weaken.
People in the area are warned that isolated rainfall totals of up 60mm are possible as the system moves out of the Kimberley region.
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