Western Australia’s worst flooding on record has spread as authorities relax road rules so essential supplies can reach the nation’s north-west.

Emergency evacuations continued in the Kimberley region on Thursday, as the Fitzroy River’s flood peak bore down on tiny Noonkanbah.

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Helicopters plucked anxious residents from the sodden outstation as evacuations continued, with three Australian Defence Force planes arriving 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,” state Emergency Services Minister Stephen Dawson said.

“This situation is still changing and it’s proving to be extremely challenging.”

About 60,000 cubic metres of water a second is flowing down the swollen Fitzroy River, which is expected to create a 50-kilometre-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, with dozens of people from other communities already evacuated.

“Multiple rescue missions have [also] been conducted in and around Fitzroy Crossing to rescue people from floodwaters,” Mr Dawson said.
“As of today there have been 47 requests for assistance.”

Road access to the town of Derby has been cut after flooding forced authorities to close a 700-kilometre section of the Great Northern Highway between Broome and Halls Creek, isolating the town of about 3000.

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 long will be permitted to travel through parts 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 north west Australia have access to food and essential supplies,” acting federal Transport Minister Madeleine King said.

It comes as ex-tropical cyclone Ellie continues to dump heavy rain with strong winds on the West Kimberley, where up to 400 millimetres fell in and around Broome in the past two days.

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The slow-moving weather system is hovering near Broome and was expected to remain in the area throughout Thursday, before rapidly moving south-east towards the NT on Friday.