Pop legend Michael Jackson is reported to have died of a heart attack after he was rushed to hospital in Los Angeles.

The entertainment TMZ website reports Jackson suffered a cardiac arrest earlier this afternoon and paramedics were unable to revive him.

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Earlier, a fire department official told the Los Angeles Times that Michael Jackson had been rushed to the hospital.

Steve Ruda told the newspaper on Thursday that Jackson was not breathing when Los Angeles Fire Department paramedics responded to a call at his Los Angeles home about 12:30pm.

The paramedics performed CPR and took him to UCLA Medical Center, Ruda told the paper.

Meanwhile, Michael's father Joe Jackson told E! Online he was aware of the emergency but did not know further details.

"I am in Las Vegas, but yes, people in Los Angeles called me and are with Michael and tell me he was taken to the hospital," he said. "I am not sure what's wrong. I am waiting to hear back from them."

The reports came as Jackson prepared to make a keenly anticipated concert comeback in London, his first series of shows in more than a decade and the first since his 2005 acquittal on child molestation charges.

In pictures: Michael Jackson 1958-2009

However those concerts -- billed as the "final curtain" -- had been thrown into doubt after Jackson pushed back the opening dates last month.

Organisers of the concerts had stressed the delay was not linked to Jackson's health.

Promoters and producers AEG Live said the rescheduling was done because of the "sheer magnitude" of the show and the desire for fans attending the opening nights to get the same experience planned for all 50 shows.

In a press conference from the United States broadcast over the Internet, AEG Live president Randy Phillips was asked about Jackson's health and said: "I would trade my body for his tomorrow. He's in fantastic shape."

While Jackson reigned as the King of Pop in the 1980s, his once-stellar career had been overshadowed by his colourful public behavior, his startling physical transformation and multiple allegations of child abuse.

Jackson lived as a virtual recluse following his 2005 acquittal on charges including child molestation and plotting to kidnap his young accuser.

Despite his acquittal, the trial was a body blow from which the pop music superstar struggled to recover.

Four years later, Jackson is still worshipped by fans for revolutionising music, dance and music videos at the peak of his success.

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The attention however paid to him in recent years has been less flattering, focusing on apparent cosmetic surgery -- which he denies -- his baby dangling antics and a decade of swirling child abuse allegations.