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Four military personnel are missing and feared dead after a Australian Army helicopter ditched into the ocean in a two helicopter exercise in North Queensland.
The MRH 90 Taipan helicopter was involved in Exercise Talisman Sabre, training between the Australian and US military, when it crashed off Hamilton Island in The Whitsundays about 11pm.
Deputy prime minister Richard Marles confirmed there were four air crew onboard and yet to be found but a search and rescue mission was continuing.
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Marles said there was another helicopter present, which meant a search and rescue was able to commence immediately.
"The families of the four air crew have been notified of this incident and our hopes and our thoughts are very much with the air crew and their families," told reporters in Brisbane.
"These are early days and there will be much more information to be provided about this incident but defence exercises, which are so necessary for the readiness of our defence force, are serious.
"They carry risk 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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Prime Minister Anthony Albanese said his first thoughts were with the loved ones of the missing.
"All Australians hold them in our hearts and we hold onto hope as the search and rescue teams go about their work right now," Albanese said in a joint statement with Marles.
"We have the utmost confidence in their professionalism and skill."
Defense chief Angus Campbell said their focus was on finding their people, supporting the families and the rest of their team.
"This is indeed a terrible moment," Campbell said.
"I really deeply appreciate the assistance has been provided by a variety of civil agencies, the Queensland Police, the Australian Maritime Safety Agency and the public, as well as US allies, all of whom have come together to assist and to continue the search and rescue and to find out people.
"I'll be available throughout the day in the coming days as excise director to provide updates as they become known to us to ensure that everybody is aware of what we're doing to better look after our people."
Talisman Sabre is a bilateral joint military exercise between Australia and the United States but it has expanded to 13 nations this year.
It began in 2005 and is the biggest it's been this year, involving 30,000 military personnel.
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