President Mubarak was laughing and waving at supporters in the court.
The judge presiding over the retrial of ousted Egyptian President Hosni Mubarak has withdrawn himself from the case as the trial opened in Cairo.
There were chaotic scenes as the judge said he was referring the trial to another court.
Mr Mubarak was convicted last June of conspiring to kill protesters during the 2011 revolt that ended his rule.
He was sentenced to life but a retrial was ordered in January after he appealed against the sentence.
About 850 people were killed in the 2011 crackdown.
Judge Mustafa Hassan Abdullah announced his decision at the start of the retrial at a police academy on the outskirts of the Egyptian capital.
The judge said he was referring the case to the Cairo appeals court as he felt "unease" in reviewing the case.
That court is then expected to appoint a new panel to hear the retrial.
But there was shouting in the courtroom, with relatives of protesters killed in the 2011 uprising chanting: "The people demand the execution of Mubarak!"
Also, prosecution lawyers complained that the transfer could delay the case for months and make it less likely that the former president would be convicted and sentenced.
"Egypt cannot close the door on the former regime until there is justice for the martyrs of our revolution," said Mohamed Rashwan, quoted by Reuters news agency. Stretcher again
Mr Mubarak, 84, is in poor health and currently being held in a military hospital in Cairo.
On Saturday, he was flown by helicopter to the courthouse at a police academy on the outskirts of Cairo.
State TV showed him being wheeled into the building on a stretcher, wearing a white outfit. Wearing dark glasses and with an intravenous cannula on his hand, he later waved to the courtroom from inside a cage.
His first trial, at which he also appeared on a stretcher, lasted 10 months.
Two sons of the former leader, former interior minister Habib al-Adly and six aides will also be re-tried, facing the same charges as before.