'Muhammad Ali's heart beat on even as his body shut down,' says his daughter Hana

Legendary boxer Muhammad Ali's heart kept beating for a full 30 minutes even after the rest of his body shut down, his daughter has said.

The incredible details of three-time heavyweight champion Ali's final moments were made public by his daughter Hana in an emotional post on Twitter.

"Our hearts are literally hurting. But we are so happy daddy is free now. We all tried to stay strong and whispered in his ear, you can go now. We will be OK. We love you," said Hana Ali, an author and a freelance writer.

"All of his organs failed but his HEART wouldn't stop beating. For 30 minutes ... his heart just kept beating. No-one had ever seen anything like it. A true testament to the strength of his Spirit and Will!" Hana wrote.

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— Hana Ali (@Hanayali) June 4, 2016

The 74-year-old Ali known worldwide as "The Greatest" passed away on late Friday at an Arizona hospital due to respiratory problems. His official cause of death was septic shock due to "unspecified natural causes", said the family spokesman Bob Gunnell.

The fighter had suffered for 35 years with Parkinson's disease, diagnosed three years after his retirement in 1981.

Ali received a bevy of honours during his lifetime, including the Presidential Medal of Freedom the highest civilian award of the US.