The jury in the high-profile trial of the white police officer accused of killing George Floyd was shown the stomach-churning bystander video on Monday of the death of the 46-year-old Black man.

"Nine minutes and 29 seconds. That's how long that went on," prosecutor Jerry Blackwell said of the amount of time Minneapolis policeman Derek Chauvin spent with his knee on Floyd's neck.

In the video, Floyd, handcuffed and pressed to the pavement, moans and gasps for breath while bystanders urge Chauvin to let up.

Floyd said "I can't breathe" 27 times, Blackwell said, before being loaded, unconscious, on a stretcher by medics and taken to hospital, where he was declared dead.

The jury of nine women and five men watched intently while the video was played in a hushed Minneapolis courtroom.

Chauvin was seated at the defence table, dressed in a grey suit with a blue shirt and blue tie. He looked up periodically at the video and jotted down notes on a yellow legal pad.

Chauvin, a 19-year veteran of the police force, is charged with murder and manslaughter and faces up to 40 years in prison if convicted of the most serious charge - second-degree murder.

Blackwell said in his opening statement that the 44-year-old defendant was not following police procedure and acted callously.

"You will learn that on May 25 of 2020 Mr Derek Chauvin betrayed his badge when he used excessive and unreasonable force upon the body of Mr George Floyd," Blackwell told the jury.

"That he put his knees upon his neck and his back, grinding and crushing him, until the very breath, no ladies and gentlemen, until the very life was squeezed out of him," Blackwell said.

The video of Floyd's death sparked protests for racial justice and against police brutality across the United States and around the world.

"The whole world is watching," said Ben Crump, a civil rights lawyer and attorney for the Floyd family ahead of opening statements.

"Today starts a landmark trial that will be a referendum on how far America has come in its quest for equality and justice for all," Crump said.

White House spokeswoman Jen Psaki said President Joe Biden would be among those following the trial.

"He certainly will be watching closely, as Americans across the country will be watching," Psaki said. "At the time of George Floyd's death, he talked about this as being an event that really opened up a wound in the American public."

'Overdose of excessive force'

Blackwell said he was not trying to put all police on trial, only Chauvin, who was fired from the Minneapolis police department.

"This case is about Mr Derek Chauvin," he said. "We are going to ask that you find him guilty of murder in the second-degree, murder in the third-degree and manslaughter."

The cause of Floyd's death is expected to be the central issue in the case, and a key piece of evidence is likely to be the bystander-filmed video that went viral.

Floyd died while Chauvin was arresting him for allegedly passing a counterfeit $20 bill.

Chauvin's attorney, Eric Nelson, told the jury that Floyd was under the influence of drugs at the time of his arrest and resisted being taken into custody.

"You will learn that Derek Chauvin did exactly what he had been trained to do," Nelson said.

"The evidence will show that Mr Floyd died of a cardiac arrhythmia that occurred as a result of hypertension, his coronary disease, the ingestion of methamphetamine and fentanyl, and the adrenaline flowing through his body, all of which acted to further compromise already compromised parts," he said.

Nelson urged the jury to ignore the furore surrounding the case. "There is no political or social cause in this courtroom," he said.

Crump, the Floyd family lawyer, said Chauvin's defence attorney is "going to try to assassinate the character of George Floyd."

"But this is the trial of Derek Chauvin," he said. "The facts are simple. What killed George Floyd was an overdose of excessive force."

Chauvin's trial is expected to last about a month.

The 14-member jury is racially mixed: six white women, three Black men, two white men, two mixed-race women and one Black woman.

They range in age from their 20s to their 60s and include a chemist, a social worker, an accountant and a nurse.

Police officers are rarely convicted in the United States when charges are brought and a conviction on any of the counts against Chauvin will require the jury to return a unanimous verdict.

Nelson asked to have the trial delayed and moved out of Minneapolis because of the March 12 announcement that the city had reached a $27 million "wrongful death" settlement with the Floyd family but Judge Peter Cahill rejected the demands.

Three other former police officers - Tou Thao, Thomas Lane, and J Alexander Kueng - also face charges in connection with Floyd's death.

They are to be tried separately later in the year.