Michael Jackson's children were crying and "hysterical" as their father was pronounced dead after two hours of efforts to revive him, an emergency room doctor said today.

As the manslaughter trial of Jackson's doctor resumed for a second week, emergency medic Richelle Cooper said she believed efforts to resuscitate the singer were "futile" by the time he arrived in hospital.

"My assessment when he arrived was that he was clinically dead, and given that it had been... about an hour (since he was first reported to not be breathing), resuscitation efforts would likely be futile," she said.

Cooper pronounced the 50-year-old star dead at 2:26 pm on June 25, 2009, after he was brought in to the Ronald Reagan UCLA Medical Center in Los Angeles, accompanied by his personal physician Conrad Murray.

After doing so, she went to see Jackson's children. "They were crying, they were fairly hysterical, being comforted by someone who was referred to as their nurse," Cooper told the LA Superior Court.

Cooper had already testified last week that she had been prepared to pronounce Jackson dead at 12:57 pm, when paramedics had been at his Holmby Hills mansion for nearly 30 minutes but seen no signs of life.

Murray is on trial charged with involuntary manslaughter over Jackson's death, allegedly by giving him an overdose of powerful sedative propofol to help him fight insomnia.

The "Thriller" star was rehearsing for a series of comeback shows in London at the time. Murray's defense lawyers claim that Jackson, desperate for sleep, gave himself an overdose while the doctor was out of the room.

Murray faces up to four years in jail if convicted in the trial, which started last week and is due to last five weeks.