The singer stopped breathing and suffered a massive cardiac arrest, although the exact circumstances of his death are unknown.
Paramedics failed to revive the 50 year-old and he was taken to hospital in a coma where he was pronounced dead.
His mother, brothers including Jermaine, Tito and Randy and sisters Janet and LaToya, had raced to be at his bedside.
He had been very frail in recent weeks as he struggled to prepare for a 50 concerts in London, which were due to start on July 13.
Elizabeth Taylor, one of Michael Jackson's closest friends, had planned to fly out on a private jet to attend Jackson's opening night in London, Larry King said on CNN last night.
Jackson's brother, Jermaine Jackson, told reporters during a press conference that he believed Michael had died from a cardiac arrest, but added that the exact cause of death was not known.
Investigators are likely to focus on claims the singer suffered a long term addiction to painkillers. Last month it was alleged he was struggling to make even a handful of the rehearsals for his comeback tour in Britain.
It later emerged he had been to just two out of more than 45 rehearsals.
One Jackson family source said at the time he was 'just not able to pick himself up out of the painkiller stupor' that he was in.
