CNN:
Fire Capt. Steve Ruda told CNN a 911 call came in from a west Los Angeles residence at 12:21 p.m. and the patient was treated and transferred to the UCLA Medical Center.
TMZ were the first to run with the story of his apparent death:
We've just learned Michael Jackson has died. He was 50.
Michael suffered a cardiac arrest earlier this afternoon at his Holmby Hills home and paramedics were unable to revive him. We're told when paramedics arrived Jackson had no pulse and they never got a pulse back.
A source tells us Jackson was dead when paramedics arrived.
Twitter has about 1,000 results per minute coming through on the topic.
Edit: TR, glad you didn't go with "RIP MJ" otherwise I think the forum might've collapsed (even more than usual).