Michael Jackson's friends and associates expressed shock and grief over the U.S. pop star's unexpected death Thursday at age 50.

Jackson fell into a coma at his Los Angeles home and could not be revived by paramedics called to the scene. He was pronounced dead at UCLA Medical Center. Police are investigating the circumstances of his death and an autopsy on his body is planned.

I can't stop crying over the sad news, People.com quoted Jackson's fellow 1980s pop-culture icon Madonna as saying, "I have always admired Michael Jackson. The world has lost one of the greats, but his music will live on forever! My heart goes out to his three children and other members of his family. God bless."