The singer was taken to an LA hospital after having a heart attack.
The Los Angeles Times reports that Michael was not breathing when paramedics arrived at his home.
Captain Steve Ruda told the paper paramedics responded to a call at the star's home around 8:26pm.
They performed cardiopulmonary resuscitation on him and took him to UCLA Medical Center.
The paper says Michael fell into a coma before he arrived.
His sister La Toya was apparently seen running into the hospital sobbing.
A UCLA spokesman says that due to patient confidentiality, it can't comment on or confirm the reports.
The singer was due to begin a series of comeback concerts at London's O2 arena on 13 July.
He is survived by children Michael Joseph Jackson Jr, Paris Michael Katherine Jackson and Prince 'Blanket' Michael Jackson II.
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