Ali's family: World can come say goodbye to 'The Greatest'

A public funeral and memorial service will be held to honour boxing legend Muhammad Ali, and his family says 'the world is invited to say goodbye.'

Ali, a three-time world heavyweight champion who was an iconic figure of the 20th century, died on Friday at the of age 74 after a long battle with Parkinson's disease.

He was admitted to a hospital in Phoenix this week after suffering from respiratory problems, but the official cause of death was 'septic shock due to unspecified natural causes', a family spokesman revealed.

World leaders, sports personalities, celebrities and fans around the world paused to remember "The Greatest," whose three-decade long career produced several unforgettable fights.

On Sunday, Ali's relatives will accompany his body from Scottsdale, Arizona to Louisville, his hometown in the southern state of Kentucky.

After a private family funeral on Thursday, Ali's coffin will be transported through the streets of Louisville on Friday; a public memorial service will be held at an arena, with former President Bill Clinton among the celebrities expected to offer eulogies.

The procession has been organised to "allow anyone that is there from the world to say goodbye," family spokesman Bob Gunnell told reporters.

Ali's daughter Hana Ali wrote on Twitter: "Our hearts are literally hurting. But we are happy daddy is free now."

A man who fought for us: Obama

The sentiment of Ali's family was shared by countless others around the world as tributes poured in.

US President Barack Obama wrote a detailed, heartfelt letter about what Ali represented.

"In my private study, just off the Oval Office, I keep a pair of his gloves on display, just under that iconic photograph of him -- the young champ, just 22 years old, roaring like a lion over a fallen Sonny Liston," the president wrote.

"I was too young when it was taken to understand who he was -– still Cassius Clay, already an Olympic Gold Medal winner, yet to set out on a spiritual journey that would lead him to his Muslim faith, exile him at the peak of his power, and set the stage for his return to greatness with a name as familiar to the downtrodden in the slums of Southeast Asia and the villages of Africa as it was to cheering crowds in Madison Square Garden," Obama continued.

Obama added that "the Ali I came to know," was not just "as skilled a poet on the mic as he was a fighter in the ring, but a man who fought for what was right. A man who fought for us."

"He stood with King and Mandela; stood up when it was hard; spoke out when others wouldn't," Obama said.

World leaders offer tribute

Cuba's President, Raul Castro

"We will never forget his chivalry and ethics, his rejection of war and defence of peace, his respect for and friendship with the companion Fidel and the great boxer born in Cuba that was Teofilo Stevenson."

Turkey's President, Recep Tayyip Erdoğan

"Muhammad Ali,who passed away yesterday, was an extraordinary athlete and a remarkable man of good deeds who conquered the hearts of millions."

British Prime Minister, David Cameron

"Muhammad Ali was not just a champion in the ring - he was a champion of civil rights, and a role model for so many people."

Jordan's King Abdullah II

"The hero of a generation and a legend of our time."

Pakistan's Prime Minister, Nawaz Sharif

"A shining example of defying the odds with perseverance and a positive attitude."

India's Prime Minister, Narendra Modi

"RIP Muhammad Ali. You were an exemplary sportsperson & source of inspiration who demonstrated the power of human spirit & determination."​