Veteran US senator and war hero John McCain - a towering figure in American politics for decades - has died at age 81 after losing his battle with brain cancer.
"Senator John Sidney McCain III died at 4:28pm on August 25, 2018," his office said in a statement. "With the senator when he passed were his wife Cindy and their family.
John McCain became an outspoken critic of Donald Trump. Source: AAP
"At his death, he had served the United States of America faithfully for 60 years."
His death comes a day after his family announced he had stopped treatment for the aggressive illness.
McCain spent more than three decades in the upper chamber of Congress, looming large in debates over war and peace and the moral direction of the nation.
The Navy fighter pilot spent years as a prisoner of war in Vietnam after being shot down while on a bombing mission over Hanoi.
John McCain is greeted by President Richard Nixon 1973 after he spending more than five years in a Vietnamese prisoner of war camp. Source: AAP
He lost the 2008 presidential election to Barack Obama, and was pilloried for selecting controversial Alaska politician Sarah Palin as his vice presidential running-mate.
Obama praises McCain's courage
President Donald Trump, who clashed with McCain over Obama-care and dealings with Russia, offered his "deepest sympathies and respect" to the Republican Senator's family.
Former president Barack Obama praised his political rival.
"Few of us have been tested the way John once was, or required to show the kind of courage that he did. But all of us can aspire to the courage to put the greater good above our own," he said in a statement.
"We shared, for all our differences, a fidelity to something higher - the ideals for which generations of Americans and immigrants alike have fought, marched and sacrificed.
John McCain is remembered for defending his opponent Barack Obama as a "decent family man" during the 2008 presidential campaign. Source: AAP
"We saw our political battles, even, as a privilege, something noble, an opportunity to serve as stewards of those high ideals at home, and to advance them around the world."
Former US President George W Bush paid an emotional tribute to McCain.
"Some lives are so vivid, it is difficult to imagine them ended. Some voices are so vibrant, it is hard to think of them stilled," Bush's statement read.
"John McCain was a man of deep conviction and a patriot of the highest order.”
On Friday, Republican Mitt Romney said he was "blessed and humbled" to have been friends with McCain.
"No man this century better exemplifies honour, patriotism, service, sacrifice and country first than Senator John McCain," he said.
"His heroism inspires, his life shapes our character."
Trump critic
With no more elections to run, since 2016, he was a rare and outspoken Republican critic of President Donald Trump.
Known for his combustible temper, he accused the 45th president of "naivete," "egotism" and of sympathising with autocrats.
John McCain ran for president twice in 2000 and 2008. Source: AAP
Following Trump's recent summit with Russian President Vladimir Putin, McCain caustically described the US leader's behaviour as "one of the most disgraceful performances by an American president in memory."
That earned him the ire of Trump, who regularly blamed McCain for his failure to reform Obama-era health care laws and refused to say his name when signing the eponymous "John S. McCain National Defense Authorisation Act."
'Friend of Australia'
Prime Minister Scott Morrison also paid tribute to Senator John McCain as a "true friend of Australia".
"He was a man of great courage and conviction. Our thoughts and prayers go out to his wife, Cindy, and all the McCain family during this time."
Senator McCain visited Australia only last year delivering an extraordinary speech in Sydney urging Australia's leaders to maintain its alliance with the US during the Trump presidency.
"I realise that some of President Trump's actions and statements have unsettled America's friends," Senator McCain said in his address at the State Library in May last year. "They have unsettled many Americans as well. There is a real debate underway now in my country about what kind of role America should play in the world. And frankly, I do not know how this debate will play out."
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 wrote on twitter.
"People who love justice, democracy, freedom and courage will mourn this loss of an American legend."
Opposition leader Bill Shorten said John McCain was a "true patriot".
"US politics will be poorer for his passing but it is better because of his contribution," he tweeted.
