A “massive” disaster relief operation is in full swing in Western Australia’s Kimberley region, as authorities reveal it could take more than a year to repair a major bridge on the state’s only road north.

Dozens of aircraft are flying aid into towns and Indigenous communities, including flood-ravaged Fitzroy Crossing where the airstrip is now able to handle large planes.

Fire and Emergency Services Commissioner Darren Klemm said more than nine tonnes of food and 10 boxes of medical supplies had been flown into Fitzroy Crossing.

“This is a massive operation under way to get essential supplies into that community and its surrounds,” he told reporters on Tuesday.

Mr Klemm said there were several flights in and out of the town daily and the airstrip is now dry enough to land larger aircraft, which will significantly increase capacity to resupply.

“I want to reassure the people in the Kimberley region we bringing a significant amount of food into the region to ensure we have adequate supplies,” he said.

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A barge carrying five truck-trailers of food will arrive in Broome on Wednesday with some to be transported by sea to isolated Derby, which is down to two days’ worth of supplies.

The Great Northern Highway south of Broome has been partially reopened, with access restricted to the transport of essential supplies.

Authorities, with assistance from the Australian Defence Force, have started the damage assessment and clean-up operation in the areas they can access.

It’s hoped some people will be able to start returning to their homes, but many areas remain inaccessible and others have no drinking water or power.

Workers are helping Indigenous people to fill in forms for financial assistance.

It comes as engineers prepare to assess damage to main roads and bridges, with hopes the highway from the Derby area to Fitzroy Crossing can reopen later in the week.

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Emergency Services Minister Stephen Dawson said significant damage to the Fitzroy Crossing bridge, linking the only road transport to the state’s north, could take years to repair.

Mr Dawson said state authorities had started looking at old flood crossings for use as a stop-gap measure, and are talking to the ADF about building a temporary bridge.

Throughout the emergency more than 280 people were evacuated from flood-affected towns and communities, with about 175 people in evacuation centres or hotels.

“This has been an unprecedented situation for WA, its the worst flood of its kind in our history,” Mr Dawson said.

“It is challenging and not something we’ve had to deal with before to this extent.”

He acknowledged many had been frustrated with the initially slow response to the emergency, which was often delayed by wild weather from ex-tropical cyclone Ellie.

Flood waters have now peaked in the Fitzroy River catchment.

The record-breaking river flow, which brought an island sea 50 kilometres wide in some areas, is now flowing out into the Indian Ocean.

Meanwhile, Mr Dawson confirmed crocodiles had been spotted near flooded Willare.

“It is a part of the world where there are animals who can kill or take a bite out of you, so please do be careful in the waters,” he said.

–AAP