Two of Michael Jackson's children watched as the doctor charged over the singer's death tried frantically to revive him in the bedroom of his rented mansion, a bodyguard said.

Faheem Muhammad told the Los Angeles court last night that Dr Conrad Murray appeared panicked as he performed chest compressions on the singer on a bed.

Mr Muhammad said the doctor asked at one point whether anyone knew CPR.

The guard said he saw Jackson's children Prince and Paris watching their father on the bed with his eyes and mouth wide open. He said Paris was crying on the floor and he eventually escorted the children from the room.

The evidence came during a preliminary hearing to determine if Murray, Jackson's personal doctor, will be tried on a charge of involuntary manslaughter.

Authorities argue that Murray gave Jackson a lethal dose of the powerful anaesthetic propofol and other sedatives in the bedroom of the mansion before he died on June 25 2009.

Earlier a choreographer who worked with Jackson on his ill-fated concert tour told the court he clashed with Murray and others over the superstar's health six days before he died.

Kenny Ortega said he was summoned to 50-year-old Jackson's home a day after letting the singer skip rehearsal because he seemed sick.

Murray and others suggested Jackson should not have been sent home because he was physically and emotionally fine, Mr Ortega said, adding he was told not to try to be Jackson's doctor or psychiatrist.

Deputy district attorney David Walgren said in his opening statement that Jackson was already dead when Murray summoned help and tried to conceal his administering of propofol to the pop star, ordering a bodyguard to collect items before paramedics were called.

Later in the hearing, Mr Ortega said Jackson had gone home early from rehearsals on June 19.

"He didn't look well at all," he said. "Michael was chilled and soft-spoken. ... He wasn't in the kind of condition to be at rehearsal."

Mr Ortega also said Jackson appeared lost.

"It was scary. I couldn't put my finger on it," he said. "I said, 'Michael, is this the best place for you to be or do you want to go home and be with your family?'. He said, 'Would you be OK with that?'. I said, 'OK', and he left."

The next morning, Mr Ortega said, he was called to Jackson's home, where he was confronted by Murray, Jackson, the star's manager Frank DiLeo, and Randy Phillips, head of AEG, the company producing Jackson's This Is It comeback tour.

"It quickly became clear that the meeting was about me," Mr Ortega said. "Dr Murray was upset that I had sent Michael home the night before and didn't allow him to rehearse."

Mr Ortega, who later directed the concert film This Is It, based on rehearsal footage, said the pop star was in good spirits throughout most of the rehearsals and was excited about the progress being made in preparation for the London shows.

He recalled his last conversation with Jackson.

"Michael said, 'I know you love me and care about me. You don't have to worry about me. I'm fine', and he gave me a big hug," Mr Ortega said.

On cross-examination, defence lawyer Ed Chernoff asked Mr Ortega if he had ever seen anyone having withdrawals from drugs, and the witness said he had not.

Another witness, Jackson's personal assistant Michael Amir Williams, described Murray calling him on the day the superstar died and frantically asking him to get help from bodyguards for Jackson, who was in a bedroom.

Murray told him the singer had a "bad reaction" and that immediate help was needed, but did not ask him to call 911, Mr Williams said, referring to the number for emergency services.

Mr Williams described the chaotic scene at the mansion and hospital and recalled the heartbreaking moment when Mr DiLeo told the children their father was dead. Mr Williams said he and Murray and everyone else were crying.

Jackson's mother Katherine, his sister LaToya and his brother Jackie attended the hearing, where Murray sat taking notes.

Murray had been giving Jackson propofol, an anaesthetic normally administered in hospital settings, six nights a week for about two months before his death, the prosecutor said in his opening statement.

Murray's lawyer declined to give an opening statement.

At the end of the multi-day hearing, a judge will determine whether there is enough evidence for Murray to stand trial.

The Houston, Texas, cardiologist has pleaded not guilty and his lawyers have said he did not give Jackson anything that should have killed him.

Mr Walgren said he would rely on Murray's statements to police, as well as text messages, phone records and expert evidence to show the doctor should stand trial.

He said evidence would show Murray waited at least 21 minutes to call an ambulance and ordered a bodyguard to help him clean up evidence before summoning help.

In the most favourable scenario, Mr Walgren said, Murray waited at least nine minutes before calling paramedics.

Mr Walgren also plans to call several experts whom he said would tell the court "there are a number of actions displayed by Dr Murray that show an extreme deviation from the standard of care".

The prosecutor also said he would call a bodyguard who would say that Murray ordered him to collect items from Jackson's bedroom.