Search and rescue crews have found debris in the search for four Australian defence helicopter crew who are feared dead after their aircraft went down off Hamilton Island in Queensland late last night.

The search and rescue operation has been underway for the best part of the last 18 hours.

Talisman Sabre Exercise Director Brigadier Damian Hill spoke to reporters on Saturday afternoon in Brisbane and confirmed four people were on-board the aircraft when it went into the ocean.

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"Defence can confirm there were four people on board at the time of the incident and sadly at this stage those personnel have yet to be found," Hill said.

"It is the defence's priority to look after those families, their members, their teammates and those that know them.

"Our thoughts, and mine in particular, are with the missing servicemen, their teammates and their families, and especially the search and rescue teams."

"We'll continue to work with local emergency services to continue the search."

Officials said two MRH-90 Taipan helicopters were flying in formation last night at about 11pm.

When the crew of one of those aircraft realised something had gone wrong with the other aircraft, they began the search operation immediately.

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Multiple agencies are involved in the search, including police.

The crash occurred during the Talisman Sabre military exercises, some of which are taking place off the coast of North Queensland.

The US is part of the military operation, as well as several other nations, which involves more than 30,000 personnel.

As soon as the search got underway, the next of kin and the family of the four personnel were informed.

Earlier today, Defence Minister Richard Marles and the Chief of Defence Angus Campbell spoke to reporters and offered their support to the families.

"Defence exercises, which are so necessary for the readiness of our defence force, are serious. They carry risk," Campbell said.

"And as we desperately hope for better news during the course of this day, we are reminded about the gravity of the act which comes with wearing our nation's uniform.

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"This is indeed a terrible moment."

Earlier on Saturday, a barge was filmed pulling wreckage from an area off the coast of Queensland.

Search and rescue crews had noticed debris in an area to the south of Hamilton Island.

Specialist divers are expected to come to the area around Hamilton Island as part of the search.

The MRH-90 aircraft are being phased out by the defence force, after one went down off the coast of New South Wales near Jervis Bay in March.

At the time, it had 10 personnel on board but all were able to make their way out.

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