The coffin of Muhammad Ali has begun its journey across the boxing great's home city of Louisville, Kentucky as fans and loved ones say a final farewell to "the greatest".
Thousands of people have lined the streets for the procession which is making its way past the Muhammad Ali Centre before continuing across the city to Cave Hill Cemetery for a private burial.
The casket, covered in a cloth bearing Arabic writing, was placed into a limousine by pallbearers before leaving the funeral home.
World leaders and celebrities will be among 18,000 people expected to attend the funeral at the KFC Yum! Centre, with the ceremony broadcast to millions of viewers around the world.
Former US president Bill Clinton will deliver a eulogy, while Ali's widow Lonnie and two of his nine children, daughters Rasheda and Maryum, will also address the congregation.
Former world heavyweight boxing champions Lennox Lewis and Mike Tyson and Hollywood actor Will Smith, who portrayed Ali in the 2001 film about the boxer's life, are among the pallbearers.
Speaking ahead of the funeral, Lewis said it was a "privilege" and an "honour" to be involved in the ceremony.
Huge crowds gathered in sweltering temperatures as the hearse paused briefly outside the Muhammad Ali centre, where fans chanted "Ali! Ali!".
Some of Ali's family and friends in the cars following the hearse waved to people watching from the roadside.
The coffin passed Ali's childhood home and travelled along Muhammad Ali Boulevard as part of the procession.
Fans have travelled to Louisville from around the world to honour Ali in his home city.
US president Barack Obama, who will miss the funeral to attend his daughter Malia's high school graduation ceremony, described Ali as "an icon" and a "personal hero" who transformed "not just the world of sport, but the world as a whole".
In a video message, he said: "It's very rare when a figure captures the imagination of the entire world. It's even rarer when that figure does so by being open and funny and generous and courageous.
"He was one of a kind. In my book, he'll always be the greatest."
Mr Obama and his wife Michelle are sending a letter to be read at the service, where White House senior adviser Valerie Jarrett - who knew Ali personally - will represent the president.
American actor Billy Crystal and Malcolm X's daughter Attallah Shabazz will speak at the funeral, while King Abdullah II of Jordan is expected to be among the congregation.
It was reported Turkish president Recep Tayyip Erdogan, who has been in Louisville and was expected to attend the funeral, had cut short his visit amid claims of a rift with the ceremony's organisers.
Mr Erdogan was initially due to address the funeral but was later removed from the list of speakers after other names were added.
The pallbearers include Jerry Ellis - the brother of Jimmy Ellis, Ali's former sparring partner and fellow world heavyweight champion - and Ali's cousins John Grady and Jan Wadell, nephew Ibn Ali, former brother-in-law Komawi Ali and family friend John Ramsey.
The funeral will be live-streamed on the internet and is also being shown at London's 02 Arena, the site of his I Am The Greatest Exhibition.
Some ticket-holders for the funeral have been criticised for trying to profit from the free event by selling tickets online.
Ali family spokesman Bob Gunnell said he was "personally disgusted" at attempts to profit from Ali's funeral and urged people not to buy the tickets.
A traditional Islamic prayer service was held for Ali on Thursday at Freedom Hall, where Ali made his professional debut with victory over Tunney Hunsaker in 1960.