George Floyd's family take a knee in Minneapolis
Lawyer Ben Crump (left), the Reverend Al Sharpton (C) and relatives of George Floyd take a knee in Minneapolis on March 29, 2021(AFP)

Lawyer Ben Crump quietly switched knees. The Reverend Al Sharpton needed some assistance. For eight minutes and 46 seconds on Monday relatives and lawyers of George Floyd took a knee to mark how long a white policeman knelt on the neck of the African American, who died of asphyxiation.

Their protest began at 8.46 am in Minneapolis, Minnesota, the US city where Derek Chauvin, 44, is on trial for murder and manslaughter after pinning Floyd -- on his stomach, with his hands cuffed behind his back -- to the ground.

In bystander footage Floyd can be heard pleading that he cannot breathe and loses consciousness. A coroner later ruled that he suffocated to death.

"We take it, a knee, for eight minutes and 46 seconds. And we want you to think up during that time, why Chauvin didn't in that time get his knee out," Sharpton, a longtime civil rights activist, told media.

The video of Floyd's death went viral, and his killing sparked a historic wave of anger in the United States and around the world against racism and police brutality against minorities.

Sharpton and Crump, who specializes in police brutality cases against African Americans, had gathered alongside Floyd's brothers and his nephew in the square across from the court house where opening arguments in the extraordinary trial began Monday.

Crump pointed to American football player Colin Kaepernick, who was the first person to take a knee -- during the national anthem at a game in 2016 -- to protest police violence again Black people.

Kaepernick paid for his peaceful protest with the loss of his career, becoming a favored target of former US president Donald Trump.

"Remember when Kaepernick kneeled, America got outraged. But Kaepernick did not kill nobody," Crump recalled.

The final seconds tick down, and the protesters stand to cries of "No justice, no peace."

"That gave you an idea of how long Chauvin had George Floyd down," said Crump.

"It had to be intentional, that's the case we make."