The 16-year-old also recounted the harrowing scenes on the day Jackson died in 2009, recalling how his younger sister Paris was "screaming" as doctor Conrad Murray was trying to revive her father.
"He just wished he had more time for rehearsals," he told the wrongful death trial, in which the Jackson family accuses AEG Live of negligently hiring Murray to care for the star for his doomed "This Is It" shows.
Murray was convicted of involuntary manslaughter in 2011 for having given Jackson an overdose of the anesthetic propofol, to help him cope with chronic insomnia as he rehearsed for the series of 50 planned London shows. Previous testimony at the manslaughter trial, and at the current civil case, has heard details of how the self-styled King of Pop's state of health deteriorated rapidly in the months before his death.
On Wednesday -- a day after the fourth anniversary of Jackson's death -- his son Prince said the singer was upset on the phone "a lot of time," most of the time with AEG Live chief Randy Phillips.
"He would cry sometimes. He said: 'They're gonna kill me, they're gonna kill me.'" Asked who he was talking about, he said: "People in AEG, Randy Phillips."
The teenager was dressed in a dark suit and tie, with long hair brushed behind his ears. He appeared reasonably relaxed, smiling as some videos and photos of the family were shown in court.
The 16-year-old, the highest-profile witness to testify since the civil trial started in late April, recalled June 25, 2009, the day his father died at his rented Holmby Hills mansion outside Los Angeles.
"I was downstairs in the sitting room. I heard screaming upstairs. I saw Dr Conrad, (personal chef) Kai (Chase) looked nervous and said 'Dr. Murray wants you upstairs.'
"I ran upstairs and I saw Dr Murray doing CPR on my dad. Dr. Murray was screaming while doing CPR. Then my sister came upstairs. She was screaming all the time saying she wants her dad," he added. Appearing to fight back tears, he recalled how the children followed the ambulance which took Jackson to hospital, in a separate car.
"My dad always told us that angels were looking after him.
At the hospital, "Dr. Murray said 'Sorry kids, dad is dead. We just cried," he told the jury. Jackson's lawyers have called a series of AEG executives -- including Phillips -- and experts as witnesses over the last two months, and are expected to hand over to the AEG defense in the near future.
His son's powerful testimony was likely an attempt to make a personal appeal to the 12-person jury before main Jackson family lawyer Brian Panish closes their side of the case.
During the testimony Wednesday, Panish showed a lot of pictures of the children, including a video shot at Christmas in which they are asked what they want to do when they are grown up. In one clip Blanket -- now 11 years old -- says "I don't know," and Paris talks about gymnastics and "helping the poor."
Prince told the court he wants to study film and business or mechanical science and business at the University of Southern California (USC).
Of his father, he said: "He wanted to know what we were learning, how we were doing at school and how we would use that to better the world. He always said you have to be creative and think with the right side of your brain." Jackson's 15-year-old daughter Paris was also originally listed among witnesses due to be called. But it is now thought unlikely she will testify, after she was hospitalized earlier this month following a suicide attempt. Her elder brother was asked about his sister at Wednesday's hearing.
"She was my dad's princess," he recalled.