PM remembers Black Hawk sacrifice

Malcolm Turnbull has honoured the sacrifice of those lost in the worst peacetime defence incident since the 1960s.

The prime minister on Sunday visited the Townsville memorial marking 20 years since two Black Hawk helicopters collided during a terrorism exercise.

Eighteen Special Air Service Regiment soldiers and three aircrew from the Army's 5th Aviation Regiment died.

Joined by wife Lucy and local member for Herbert Ewen Jones, Mr Turnbull laid a wreath, standing in silence with his hand on his heart.

"We remember them," he told reporters after inspecting plaques with the names of those lost.

"We stand in solidarity with the families and friends they left behind."

Mr Turnbull cited the RSL motto - the price of liberty is eternal vigilance.

"That vigilance comes with a cost. Those young men paid that price and we honour them," he said.

He also recognised the risks and dangers the rest of the defence force undertakes to keep Australians safe everyday.

"It is a very dangerous business defending Australia, in war and indeed in training."

His visit follows Opposition Leader Bill Shorten's earlier on Sunday ahead of a ceremony to mark the disaster in which Mr Jones was invited to represent the Commonwealth.