From left, former first lady Laura Bush, former President Bill Clinton, former Secretary of State Hillary Clinton, former vice president Dick Cheney and his wife Lynne and former vice president Al Gore arrive at a memorial service for Senator John McCain at Washington Nationals Cathedral in Washington. Picture: Pablo Martinez Monsivais/AP/African News Agency (ANA)

Washington - Former US presidents Barack Obama and George W Bush prepared on Saturday to honour the late John McCain, the longtime senator from Arizona and Vietnam war hero whose bids for the White House were dashed by the two men.

McCain's body, which had lain in state at the US Capitol, arrived at the Washington National Cathedral after his procession first stopped at the Vietnam Veterans Memorial, where his wife, Cindy McCain, laid a wreath to honour those who died in the war.

Obama and Bush, a Democrat and a Republican, were joined by a who's who of US political leaders, Vietnam-era officials and dignitaries paying tribute to the statesman and former prisoner of war, who died Aug. 25 of brain cancer, days shy of his 82nd birthday.

President Donald Trump, who feuded publicly with McCain and criticised his war record, did not attend. Members of his administration, including his daughter Ivanka, son-in-law Jared Kushner, and national security adviser John Bolton were present.

McCain's family had made clear that Trump was not welcome at memorial services in Arizona and Washington or at Sunday's private burial service in Annapolis, Maryland, at the US Naval Academy. McCain was a member of the Academy's Class of 1958.

Cindy McCain, wife of, Senator John McCain accompanied by White House Chief of Staff John Kelly, left, and Defense Secretary Jim Mattis, second from left, lays a wreath at the Vietnam Veterans Memorial in Washington. Picture: Andrew Harnik/AP/African news Agency (ANA)

Trump spent the morning sending tweets about other subjects.

Inside the cathedral luminaries including comedian Jay Leno, former Secretary of State Madeleine Albright, former Senator Bob Dole and others visited with other leaders while a powerful pipe organ played music in the background.

McCain was a leading voice for revamping the country's immigration, campaign finance and environmental laws. But it was his military service, punctuated by years as a prisoner of war in North Vietnam, that molded McCain's political life.

McCain, who rose to the rank of captain in the US Navy, was shot down over Hanoi while on a bombing mission in 1967.

Held as a prisoner until 1973, McCain was tortured by his North Vietnamese captors in a jail that Americans dubbed the "Hanoi Hilton."