Cedars-Sinai Medical Centre spokeswoman Sally Stewart says Murphy was pronounced dead at 10.04am on Sunday (local time).
Murphy was transported to the hospital after the Los Angeles Fire Department responded to a call at 8am at the home Murphy shared with her husband, British screenwriter Simon Monjack, in the Hollywood Hills.
Assistant Chief Coroner Ed Winter says the cause of Murphy's death "appears to be natural."
He says Murphy apparently collapsed in the bathroom, and authorities are looking into her medical history.
Winter says Murphy's family is cooperating with the coroner's investigation. He says an autopsy is planned for Monday or Tuesday.
Murphy starred films including Clueless, 8 Mile, and Don't Say a Word.
