LOS ANGELES, California -- An autopsy on entertainer Michael Jackson has been scheduled for Friday and results are expected by afternoon, according to the Los Angeles, California, coroner's office.

The "King of Pop," who was preparing for a comeback tour, died Thursday at age 50.

Jackson, under apparent cardiac arrest, was taken from his home by paramedics to Ronald Reagan UCLA Medical Center, where a team of physicians tried to resuscitate him for more than an hour, said Jackson's brother Jermaine. He said the music idol was pronounced dead at 2:26 p.m. (5:26 p.m. ET).

Another one of Jackson's six siblings told CNN that he learned of Jackson's death through his manager, Frank Dileo.

"Frank told me that Michael last night was complaining about not feeling well. He called to tell him he wasn't feeling well," Marlon Jackson said. "Michael's doctor went over to see him, and Frank said, 'Marlon, from last night to this morning, I don't know what happened.' When they got to him this morning, he wasn't breathing." Fire Capt. Steve Ruda told CNN that a 911 call came in from a west Los Angeles residence at 12:21 p.m. Jackson was treated and transferred to the UCLA Medical Center, Ruda said.

At the hospital, security guards blocked every entrance to the emergency room. Even hospital staffers were not permitted to enter. A few people stood inside the waiting area, some of them crying.

Detectives from the Los Angeles Police Department remained at Jackson's home late Thursday, with some officers providing crowd control outside as fans gathered in surrounding streets.

At one point, three tow trucks arrived at the residence and a silver BMW with Texas license plates was later removed. No reason was given by police.

During a career that began at age 5 singing with his brothers, Jackson had numerous No. 1 hits. "Thriller" is the best-selling album of all time, at an estimated 50 million copies worldwide.

But after dominating the popular music scene for years, Jackson became reclusive and mired in scandals that include molestation charges. He was acquitted after a well-publicized trial in Santa Maria, California, in March 2006.

Last year, Jackson announced a comeback tour that was to start in July. When some of the shows were postponed till next year, rumors spread that the entertainer was weak and suffering from skin cancer.

However, Marlon Jackson said he last saw his younger brother at a May 14 family gathering and he "looked great."

"He was looking well. He was getting ready to go into rehearsals for his tour. I don't know what happened," Marlon Jackson said.

"Janet Jackson is grief-stricken and devastated at the sudden loss of her brother," said her manager, Kenneth Crear. "She is ... flying immediately to California to be with her family."

A large crowd gathered outside the hospital, according to video footage. Michael Jackson fans across the world reacted with sadness.

Some, including actress Elizabeth Taylor and musician Stevie Wonder, were too distraught to issue statements.

Producer Quincy Jones, who helped Jackson craft his hit albums "Off the Wall" and "Thriller," said, "I am absolutely devastated at this tragic and unexpected news."

"For Michael to be taken away from us so suddenly at such a young age, I just don't have the words," Jones added in a statement.

Jackson's music continues to be heard throughout the world "because he had it all -- talent, grace, professionalism and dedication," Jones said. He called Jackson a consummate entertainer, whose legacy will be felt around the world.

"I've lost my little brother today and part of my soul has gone with him," Jones said.

Berry Gordy, producer and founder of Motown Records, said Jackson's death was "like a bad dream."

"As a kid, Michael was always beyond his years. He was an innovator. He was a genius at what he did," Gordy said. "He had a knowingness about him. At 9 years old, when I first started working with him, he seemed to me like he had been here before. He was just so knowledgeable about life."

Lisa Marie Presley, Jackson's former wife, said she was "shocked and saddened" by his death.

"My heart goes out to his children and his family," she said.

Jackson is survived by his three children, Prince Michael I, Paris and Prince Michael II.