Boxing legend Muhammad Ali has been placed on life support at a Phoenix, Arizona hospital after his health deteriorated on Friday.

Ali was hospitalised on Thursday for a respiratory issue.

The three-time heavyweight champion, who retired from the ring in 1981 after a defeat to Trevor Berbick, has been hospitalised multiple times in recent years.

He spent time in hospital in 2014 after suffering a case of mild pneumonia and again in 2015 for a urinary tract infection.