Religious and political leaders of many stripes joined the sports world and tens of thousands of ordinary mourners today to bid farewell to Muhammad Ali, the boxing champion who jolted America with his showmanship and won worldwide admiration as a man of principle.

Ali, a once-controversial convert to Islam who lost three prime years of his boxing career for refusing US military service during the Vietnam War, died a week ago at age 74 as one of the most respected men in the United States.

Fans chanting "Ali!" and throwing flowers lined the streets of Louisville, Kentucky, for a funeral procession. Ali's hearse snaked through the city, pausing for a huge crowed outside his boyhood home, en route to a cemetery for a private burial beneath a headstone reading simply "Ali."

A fan runs over to throw flowers on Muhammed Ali's hearse. Photo: Reuters

City officials estimated 100,000 people came out to honor Ali, many traveling from across the country and across the world. Some tossed flowers atop the hearse carrying his casket as part of an 18-car procession over 23 miles (37 km) in a memorial unlike any other in recent US history.

After Ali's body was put to rest, former President Bill Clinton and celebrities such as Billy Crystal, Will Smith and Mike Tyson were among those gathered at a 20,000-seat sports arena for an interfaith memorial service that began with Muslim prayers.

The Reverend Kevin W. Cosby, a pastor at a Louisville church, likened Ali to other ground-breaking black athletes who advanced civil rights such as baseball player Jackie Robinson, boxer Joe Louis and track star Jessie Owens.

"Before James Brown said, 'I'm black and I'm proud,' Muhammad Ali said, 'I'm black and I'm pretty,'" Cosby told a crowd the arena, referring to the 1960s R&B singer. "He dared to love black people at a time when black people had a problem loving themselves."

Pallbearers lift Muhammed Ali's coffin. Photo: Reuters

Earlier on a hot day, some 1,500 people gathered outside Ali's boyhood home in a traditionally African-American section of town. As the hearse arrived, police standing shoulder-to-shoulder cleared a path, much like a fighter's entourage clears his way to the ring.

The hearse stopped at the pink house as the people, many of whom waited in the sun for more than three hours, chanted his name.

"It was important for me to be here," said Matt Alexander, 63, who traveled from Florida. "I cried like a baby when I heard he'd died. I just didn't want to believe it because I wanted him to live forever."

Rickey Martin, 55, compared him to civil rights leader Martin Luther King Jr. as a towering figure of the 20th century.

"Ali and MLK instilled in our generation that you didn't just have to sit back and do as you were told," Martin said. "You could go to school, you get a good job. In the years after segregation ... he was an inspiration to all of us."

Dipo Akabashorun, 51, came from Lagos, Nigeria to see off Ali. "We claim him, too, as our native son. We claim him too as a Lagotian," he said.

Some foreign dignitaries attended but Turkish President Tayyip Erdogan, who went to a Muslim funeral for Ali on Thursday, cut short his visit to Louisville and did not take part in Friday's event as planned.