Engineers are frantically working to solve engine problems on the Royal Australian Navy's two largest ships, with fears the Landing Helicopter Docks (LHDs) could be out of action for several weeks.

The Canberra Class Amphibious Assault Ships HMAS Canberra and HMAS Adelaide are currently docked at Sydney's Garden Island Naval Base where maintenance crews are trying to identify and resolve issues with the LHDs' azimuth propulsion system.

Defence sources have confirmed to the ABC they currently expect the problem will take between seven and 10 days to address, but if further complications are found, the 27,000-tonne ships could remain sidelined for even longer.

The Defence Force insists the inspections have "had no impact on Navy meeting its operational tasks".

In a statement to the ABC on Monday night the Defence Department confirmed a propulsion issue had been identified on board HMAS Canberra during recent trials with military helicopters.

"As a prudent measure, the same inspections were conducted on HMAS Adelaide and identified emergent issues," it said in a statement.

"It is too early to determine the extent of this emergent work and Defence is working to identify the causes and develop a repair strategy."

Unavailable ships a 'significant failure': Feeney

Federal Opposition MP David Feeney, who sits on Parliament's Joint Standing Committee for Defence, Foreign Affairs and Trade, said it was a worrying development.

"The news that both of our major amphibious ships are unavailable for service in this Queensland cyclone period is very, very troubling and represents a significant failure," Mr Feeney said.

"The good news is that the capability gap can be filled by HMAS Choules, a vessel procured by the former Labor government in 2010, but nonetheless these amphibious ships are designed for precisely this work that they're now not able to do."

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Mr Feeney demanded the Government provide a full explanation of the problems.

"The Government does need to explain to us precisely what is the engineering problem that they're confronting, how did it happen, and I think, very importantly, will these ships be available for service in Operation Talisman Sabre [in July]."

On Monday, the Chief of Defence, Air Chief Marshal Mark Binskin, said the military was well positioned to provide immediate assistance to local communities within Cyclone Debbie's storm zone, if requested.

"We are ready and able to respond to this emergency in support of civilian emergency authorities and the residents of north-eastern Queensland once the full impact of [Cyclone] Debbie is known," he said.

As a precaution, HMAS Choules — the nominated HADR (Humanitarian Assistance and Disaster Relief) ship — left Sydney on Monday morning to head to Queensland "to be ready to support recovery efforts if required".