US Senator John McCain was a truly great man whose death is like the loss of a family member, Prime Minister Scott Morrison says.
The two-time presidential nominee died aged 81 on Sunday surrounded by family at his Arizona home, after battling brain cancer.
Mr Morrison recalled the impact Senator McCain had on people when he visited the federal parliament in 2017.
"You knew you were in the presence of a truly great man," the prime minister told reporters on Sunday.
"He embodied everything that we respect and value and love about our American friends.
"They are like family and his loss today is like the loss of a family member to us as Australians."
Mr Morrison earlier tweeted the senator was "a true friend of Australia who was committed to strengthening the alliance between our two nations".
Former prime minister Malcolm Turnbull lauded the former prisoner of war as a great friend of Australia who lived a "courageous life".
"America has never had a more heroic and determined champion," he tweeted.
"And Australia has never had a stauncher American friend. Rest In Peace."
Australia's Ambassador to the United States Joe Hockey also paid his respects to the war hero.
"How terribly sad to hear that Senator John McCain has passed away," he tweeted.
"People who love justice, democracy, freedom and courage will mourn this loss of an American legend."
Labor leader Bill Shorten lauded the "true patriot" for being a loyal friend to Australia and a defender of liberty around the world.
"US politics will be poorer for his passing but is better because of his contribution," he tweeted.
Former deputy prime minister Tim Fischer said Vietnam veterans would salute "the real bravery of John McCain", who spent more than five years as a prisoner of war after his US Navy fighter plane was shot down.
Senator McCain entered federal politics in 1983 and ran for the country's top job in 2000 and 2008.
