Many of them burst into tears as his death was announced.
Jermaine Jackson, the singer's brother, said: "This is hard. My brother, the legendary King of Pop, Michael Jackson, passed away ... It is believed he suffered cardiac arrest in his home."
"Our family requested that the media please respect our privacy during this tough time. And we all will be with you Michael, always. Love you."
In New York's Times Square, a low groan went up in the crowd when a screen flashed news that Jackson had died.
Worral said an autopsy was likely to be carried out on Friday.
Jackson's death comes four months after he announced he would perform a series of 50 shows in London in July.
The performances were seen as the beginning of a public comeback by Jackson, 50, who had spent recent years countering a series of damaging allegations about his private life.
The singer was acquitted in 2005 of charges alleging that he had committed abuses against children and that he had plotted to kidnap a youth who had filed a complaint against him.
Reverend Al Sharpton, the US civil rights activist, praised the singer's accomplishments, saying they would not be overshadowed by controversial claims.
"No controversy will erase the historic impact [Jackson had]. He learnt how to sing and dance past unfair criticism," he said.
Jackson reached the peak of his fame in the 1980s as a solo artist, after leaving his brothers in the already hugely-successful Jackson 5, later known as the Jacksons.
His 1982 album Thriller went on to become the world's then top-selling album of all time, with sales exceeding 41 million copies, cementing his image as the self-styled "king of pop".
Producer Quincy Jones, who collaborated with Jackson on three of his best-selling albums, Off the Wall, Thriller and Bad, said in a statement: "I am absolutely devastated at this tragic and unexpected news.
"For Michael to be taken away from us so suddenly at this young age, I just don't have the words."
But while Jackson's 1987 album Bad was also a strong seller and helped him maintain his position as the biggest solo musical artist in the world, critics and fans alike began to pay increasing attention to dramatic changes in Jackson's physical appearance.
Jackson repeatedly denied reports that he had had plastic surgery to alter his appearance, claiming that a rare skin condition was responsible.
His stated preference for the company of children and his friendship with a chimp also earned him critics and the nickname "Wacko Jacko".
Jackson leaves behind three children, two he had with Debbie Rowe, whom he divorced in 1999, and another from a mystery surrogate mother.
He was also previously married to Lisa Marie Presley but they divorced in 1996.