Paramedics were called to the singer’s home around midday local time on Thursday after he stopped breathing. He was pronounced dead two hours later after arriving at hospital in full cardiac arrest, said Fred Corral of the LA County Coroner’s office.
The star, who had a history of health problems, had been due to begin a series of comeback concerts in the UK on 13 July.
Concerns were raised last month when four of the concerts were postponed, but organisers insisted the dates had been moved due to the complexity of staging the show.
A spokeswoman for The Outside Organisation, which was organising the publicity for the shows, said she had no comment at this time.
Uri Gellar, a close friend of the star, told BBC News: “I’m devastated – it’s very, very sad.
“I’m still trying to hold on to the glimmer that it’s not true. It’s too surreal for me to absorb that Michael is no longer with us.”
Hip hop star P Diddy wrote on Twitter : “Michael Jackson showed me that you can actually see the beat.
“He made the music come to life! He made me believe in magic. I will miss him!”
Speaking outside the UCLA medical centre in Los Angeles, civil rights activist Rev Al Sharpton paid tribute to his friend.
“I knew him 35 years. When he had problems he would call me,” he said.
“I feel like he was not treated fairly. I hope history will be more kind to him than some of the contemporary media.”
Paramedics were called to the singer’s house in Bel Air at 1221 local time following an emergency phone call.
They performed CPR on Jackson and rushed him to the UCLA medical centre.
Crowds have gathered outside the facility, whose emergency centre has been roped off by police.
Jackson began his career as a child in family group The Jackson 5.
He then went on to achieve global fame as a solo artist with smash hits such as Billie Jean and Bad.
Thriller, released in 1982, is the biggest-selling album of all time, shifting 65m copies, according to the Guinness Book of World Records.
He scored seven UK number ones as a solo artist and won a total of 13 Grammy awards.
Neil Portnow, president of the Recording Academy, which awards the Grammys, also paid tribute: “Rarely has the world received a gift with the magnitude of artistry, talent and vision as Michael Jackson.
“He was a true musical icon whose identifiable voice, innovative dance moves, stunning musical versatility, and sheer star power carried him from childhood to worldwide acclaim.
“We are deeply saddened by this tragic news and our hearts go out to his family and to music lovers around the globe who mourn this great loss.”
“For Michael to be taken away from us so suddenly at such a young age, I just don’t have the words,” said Quincy Jones, who produced Thriller, Bad and Off The Wall.
“He was the consummate entertainer and his contributions and legacy will be felt upon the world forever. I’ve lost my little brother today, and part of my soul has gone with him.”
Family
The singer had been dogged by controversy and money trouble in recent years, becoming a virtual recluse.
He was arrested in 2003 on charges of molesting a 14-year-old boy, but was found not guilty following a five-month trial.
The star had three children, Michael Joseph Jackson Jr, Paris Michael Katherine Jackson and Prince Michael Jackson II.
He is survived by his mother, Katherine, father, Joseph and eight siblings – including Janet, Randy, Jermaine and La Toya Jackson.
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