Emergency evacuations continued in the Kimberley region on Thursday as the Fitzroy River's flood peak bore down on tiny Noonkanbah.
Helicopters plucked anxious residents from the sodden outstation as evacuations continued after three Australian Defence Force planes arrived to help with the airlift.
"People in the Kimberley are experiencing a one-in-100-year flood event, the worst flooding WA has ever seen," Emergency Services Minister Stephen Dawson told reporters.
"This situation is still changing and it's proving to be extremely challenging."
About 60,000 cubic metres of water per second is flowing down the swollen Fitzroy River, which is expected to create a 50km-wide inland sea as it spreads across the flood plain.
Looma and Willare are also under threat after the river reached a record 15.81 metres upstream at Fitzroy Crossing, home to around 1200, while dozens of people from surrounding communities have been evacuated.
Major flooding is expected at Noonkanbah from Friday into Saturday.
"Multiple rescue missions have (also) been conducted in and around Fitzroy Crossing to rescue people from floodwaters," Mr Dawson said on Thursday.
"As of today there have been 47 requests for assistance."
Road access to the town of Derby was cut after flooding forced authorities to close a 700km section of the Great Northern Highway between Broome and Halls Creek, isolating the town of about 3000 people.
Authorities say it's likely the freight route south of Broome is also impassable at low-lying Roebuck Plain and it could take many weeks for it to drain.
The emergency has prompted the authorities to temporarily tweak the rules for long road trains in WA and South Australia to ensure food and essential supplies reach WA's north and the Northern Territory.
Normally banned road trains up to 53.5 metres in length will be permitted to travel through parts of eastern WA and SA until late February.
"This temporary access will allow increased freight capacity on alternative road networks to keep essential freight moving and ensure communities in northwest Australia have access to food and essential supplies," federal acting Transport Minister Madeleine King said.
It comes as ex-tropical cyclone Ellie continues to dump heavy rain with strong winds on the Kimberley region, where falls of up to 400mm have been recorded in and around Broome over a 48-hour period.
The slow-moving weather system has moved to the southeast and is expected to move further inland towards the Northern Territory on Friday afternoon.
Parts of WA's northeast could receive up to 150mm of rain within 24 hours, creating the risk of dangerous flash flooding, the Bureau of Meteorology said.
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