Three Australian Commandos and a US soldier have been killed in a helicopter crash in Afghanistan.

The diggers were among 10 Australians from the Special Operations Task Group on the coalition forces helicopter when it went down in rugged terrain in Northern Kandahar.

The chief of the Defence Force, Air Chief Marshal Angus Houston, said the crash at 3:39am (Afghanistan time) was not the result of enemy action.

He said the seven other Australians on board the helicopter are being treated for their wounds.

"Two are very seriously wounded with one undergoing surgery and one is in intensive care at an ISAF medical facility," he said.

"These soldiers, along with one of the less seriously wounded, will be moved to the US military hospital in Bagram later today once their condition stabilises."

A NATO spokeswoman in Kabul confirmed that a US soldier was also killed in the crash.

Air Chief Marshal Houston said as operations were ongoing he was unable to provide more details, but he did confirm all three of the soldiers killed had previously served in Afghanistan.

"These three soldiers were members of a very impressive group of soldiers who were highly skilled and highly motivated," he said.

"Just last week they were involved in an operation at Shah Wali Kot which dealt a major blow to Taliban insurgents in Northern Kandahar province."

The crash was Australia's deadliest single incident in the nearly nine-year conflict. Air Chief Marshal Houston said the cause of the crash would be investigated.

The deaths bring the number of Australians who have died during operations in Afghanistan since 2001 to 16.

Earlier this month, a roadside bomb killed Sappers Jacob Moerland and Darren Smith of the Australian mentoring taskforce.

Condolences

Air Chief Marshal Houston expressed his condolences to the families of the "three fine commandos we lost this morning".

"I have nothing but admiration and respect for these very brave and committed Australians," he said.

"I ask you now to be there for each other."

Defence Minister John Faulkner said the loss of the "three courageous soldiers" was a tragedy.

"This most dangerous theatre of operations has claimed five Australian lives in just two weeks and it's with very great sadness that we are here today to inform you of these casualties," he said.

"This is a tragic day for Australia and the Australian Defence force and an absolutely devastating day for the families and friends of these young men.

"Three brave young men died today serving our nation. I assure you that the commitment, dedication and sacrifice of these soldiers will not be forgotten."

He said the wounded soldiers are receiving the best medical care.

Senator Faulkner said Australia's commitment to Afghanistan is important.

"While our mission in Afghanistan is difficult, it is vital for international stability and for the security of Australia," he said.

"Our men and women in uniform continue to do outstanding work in this demanding and dangerous environment."

He said the deaths will delay an announcement that he was planning to make tomorrow about Australia's contribution to the war in Afghanistan.

He was intending to make a ministerial statement to Parliament tomorrow, particularly about the timing of the training mission that Australian forces are involved in in Afghanistan.

Both Prime Minister Kevin Rudd and Opposition Leader Tony Abbott paid tribute to the soldiers in Parliament.

Mr Rudd said the soldiers have made the ultimate sacrifice for their nation.

"All Australians owe them a debt of gratitude for their service and sacrifice," he said.

Mr Abbott said the deaths show the high price soldiers pay in serving Australia.

"Our soldiers are made of great character," he said.

"The families... of those killed in action... will be devastated."