Police want to interview Michael Jackson's doctor after the star's family suggested he died because of a drug overdose, according to reports.The King of Pop suffered a cardiac arrest at his home in Holmby Hills and was taken to the UCLA medical centre where he was pronounced dead.
Tmz.com said Jackson received a daily injection of Demerol, a synthetic narcotic similar to morphine, but was given "too much" on Thursday.
Los Angeles police want to talk to the doctor - who lived at the star's home and administered his injections - but he has not yet been found, the entertainment website said.
Jackson's brother Jermaine Jackson confirmed the "legendary" star had passed away at the age of 50 after doctors worked for more than an hour to try to revive him.The star's body was flown by helicopter from the hospital to the LA coroner's office and a post-mortem examination is expected to take place later today.
Brian Oxman, a spokesman for the Jackson family, said the singer's relatives had been concerned about his health and had tried to take care of him for months.
"Michael appeared at rehearsals a couple of times, he was very seriously trying to be able to do those rehearsals," he said.
"His use of medications had gotten in the way, his injuries which he had sustained performing, where he had broken a vertebrae and he had broken his leg from a fall on the stage, were getting in the way."
The first reports of Jackson's death emerged on the internet and sparked a huge surge in online traffic as people searched for the latest news.
Twitter has been flooded with tributes from fans and celebrities alike including Demi Moore, Ashton Kutcher and Stephen Fry.
Moore also paid tribute to Charlie's Angels actress Farrah Fawcett, who died earlier on Thursday.
See how Jackson's famous fans reacted to his death.
A tweet from Emily Eavis, organiser of the Glastonbury music festival, said there would be tributes "all over the site all weekend".
TV channels around the world interrupted programmes to break the news of Jackson's death, while many radio stations are playing his hits back-to-back.
Singer and actress Cher paid tribute saying: "He was a great singer. You know, it's like God gives you certain gifts. And some people he gives different gifts and some people he gives more gifts.
"And this child was just an extraordinary child, touched by this ability to have people feel him and feel people. You know, he was a genius, like Ray Charles, like Stevie Wonder. They just have this gift."
Former Beatle Sir Paul McCartney described Jackson's death as "sad and shocking".
He said: "I feel privileged to have hung out and worked with Michael. He was a massively talented boy man with a gentle soul. His music will be remembered forever."
Madonna added: "The world has lost one of its greats but his music will live on forever."
Fans gathered near Jackson's childhood home in Gary, Indiana, to pay their respects to the singer who left the city years ago.
In LA, people lined the streets outside the hospital and coroner's office while others laid flowers and candles on his star on the Hollywood Walk of Fame.
Read more about how fans are paying tribute.
Office worker Yoshiko Plair, who went to the hospital as soon as she heard reports of Jackson's heart attack, said: "He changed music, he's the reason all that black music is on MTV now.
"I followed him from that first song. I'm going to mourn him today and probably for the rest of my life."
On the other side of America, fans congregated at the Apollo Theatre in Harlem, New York, where Jackson gave some of his earliest performances, to sing and dance in his memory.
Civil rights campaigner the Rev Al Sharpton was among crowds and told mourners: "I have known him at his high moments and his low moments and I know he would want us to pray for his family."
