Michael Jackson's personal physician, convicted of manslaughter for administering a lethal dose of anaesthetic to the pop singer, has been released from a Los Angeles prison.

Conrad Murray was released after serving half of his four-year sentence.

The move came under a California state plan to reduce prison overcrowding.

Murray's six-week trial grabbed global attention after Michael Jackson died unexpectedly in 2009 at the age of 50.

Reporters waited outside the jail for Murray, but he was taken out through a back exit away from view.

A few Jackson fans were also were present, one playing music from his 1982 album Thriller. 

Jackson's death prompted an outpouring of support for the so-called King of Pop after years of bad publicity, stemming from his increasingly bizarre behavior and a child molestation trial in which he was acquitted.

Today, he is the top-earning dead celebrity, according to Forbes.

Prosecutors successfully argued that Grenada-born Murray, who was hired by concert promoter AEG Live as Jackson's general practitioner, was grossly negligent in administering propofol, a drug that was used to help the singer sleep.

Murray, 60, was convicted in 2011 of involuntary manslaughter - or unintentional killing without malice - and received the maximum four-year penalty.

Murray's attorneys presented the case that Jackson had injected himself with the powerful anesthetic. A California appellate court has yet to hear oral arguments in Murray's bid to overturn his conviction.

"He's prepared to keep fighting this as long as it takes," Murray's attorney Valerie Wass said ahead of her client's release.

Murray's license to practice has been suspended in California, Nevada and Texas, each of the states where he had been able to work prior to Jackson's death.        

Murray has kept his name in the headlines during his time in prison by releasing sometimes rambling messages to the media and granting live telephone interviews within the past year.

In one instance, Murray began singing during the interview and in another he told Michael Jackson's teenage daughter Paris that he loved her like a father.