Civil rights leader Reverend Al Sharpton vowed the mass protests ignited by George Floyd's death in police custody would continue until "we change the whole system of justice" in the United States at an emotional memorial service in Minneapolis.
Mr Floyd's attorney told mourners he would find justice for the 46-year-old, who died during a 25 May arrest when a white police officer knelt on his neck for nearly nine minutes.
"It was not the coronavirus pandemic that killed George Floyd," said Benjamin Crump, who is representing Mr Floyd's family. "It was that other pandemic. The pandemic of racism and discrimination."
The crowd in Minneapolis stood in silence for the eight minutes and 46 seconds that officer Derek Chauvin spent with his knee on Mr Floyd's neck, a scene captured on videotape.
Mr Floyd's death has reignited long-felt anger over police killings of African-Americans and unleashed a nationwide wave of civil unrest unlike any seen in the US since King's 1968 assassination.
With demonstrations for racial justice sweeping through dozens of US cities and around the world, Reverend Sharpton said Mr Floyd's death would not be in vain.
"You changed the world George," the 65-year-old Baptist minister said. "We're going to keep fighting George."
"We're going to keep going until we change the whole system of justice.
"It doesn't matter if you wear blue jeans or a blue uniform you must pay for the crime you commit," Reverend Sharpton said, comparing Mr Floyd's death to that of a black New York man, Eric Garner, who also gasped "I can't breathe" as a police officer held him in a chokehold.
"We were smarter than the underfunded schools you put us in but you had your knee on our neck. We could run corporations and not hustle in the streets, but you had your knee on our neck.
"We had creative skills, we could do whatever anybody else could do, but we couldn't get your knee off our neck.
"What happened to Floyd happens every day in this country, in education, in health services, and in every area of American life. It is time for us to stand up in George's name and say get your knee off our necks."
Members of Mr Floyd's family, the Reverend Jesse Jackson, Minnesota Governor Tim Walz, Minnesota Senator Amy Klobuchar and Minneapolis Mayor Jacob Frey were among several hundred people attending the service at North Central University in downtown Minneapolis.
Many of the mourners wore masks because of the coronavirus pandemic.
Minneapolis police chief Medaria Arradondo dropped to a knee as the hearse bearing Mr Floyd's remains arrived for the service, streamed live to a large crowd gathered at the flower-covered site where Mr Floyd died.
Voices of the future
A vigil for Mr Floyd was also held in New York and was attended by thousands of people, including Mr Floyd's brother, Terrence.
"White Silence is Violence," a sign read. "Make America Not Embarrassing Again," read another.
Ten-year-old Corte Ellis held a sign he had made using a piece of cardboard from a broken-down box. He had written some of Mr Floyd's final words: "I can't breathe, I can't breathe."
"I'm here to protest for George Floyd because he didn't deserve to die," said Corte, who was accompanied by his stepfather, Timothy Walker, and almost-two-year-old brother, Cody.
Seeing the crowd stream into Cadman Plaza Park in Brooklyn, Corte said, "It's good because it tells me how many people are willing to go so far to get rights."
Mr Walker, 54, said he took the boys to the memorial because it was important for them to understand racial inequality.
Kallai Brooks, 36, attended the vigil with his wife, Alisha, 34, and their sons, ages eight and three.
"They need to know just as much as I have to know what we're facing. At the same time, as much as there are people in this world who want to do harm, there are a lot of people who care and love each other, so they have to see both sides," Mr Brooks said.
Tawana Boatwright, 33, attended the Floyd memorial with her daughters Skylar, 11, and Leia, seven.
"It's hard to explain. They don't really understand," Ms Boatwright said. "They know a man who was unarmed was killed and that's all they know. Their dad is an unarmed black man and my boyfriend is an unarmed black man."
Leia had drawn her own sign: "Black lives matter, we have voices."
"I feel happy for being here because the murder of George Floyd, it wasn't nice of the cops to do that," Leia said. "No matter what skin colour you are, you still are loved."
Three of the four Minneapolis police officers who arrested Floyd for allegedly passing a counterfeit bill made their first court appearance on Thursday to face charges of aiding and abetting his murder.
Bail was set at $US1 million ($A1.4 million) each.
The fourth policeman, Mr Chauvin, has been charged with second-degree murder and appeared before a judge last week.
'Cannot stop the call of history'
Democratic Congressman John Lewis, who marched with Martin Luther King Jr to fight segregation, echoed Mr Sharpton's hope that Mr Floyd's death could pave the way for "greater change."
"This feels and looks so different," the 80-year-old civil rights icon told CBS This Morning. "It is so much more massive and all inclusive."
Mr Lewis, who was brutally beaten on several occasions during the 1960s civil rights protests, condemned US President Donald Trump's threat to use military force against demonstrators.
"I think it would be a serious mistake on the part of President Trump to use the military to stop orderly, peaceful, nonviolent protests," Mr Lewis said. "You cannot stop, cannot stop the call of history."
I know your pain, your rage, your sense of despair and hopelessness. Justice has, indeed, been denied for far too long. Rioting, looting, and burning is not the way. Organize. Demonstrate. Sit-in. Stand-up. Vote. Be constructive, not destructive. https://t.co/YbB14dgzr9
While condemning Mr Floyd's death, Mr Trump has adopted a tough stance towards the protesters, saying they include many "bad people" and calling on governors to "dominate the streets".
Mr Trump has raised the possibility of invoking the Insurrection Act to deploy active duty troops to quell the unrest but his own defence secretary, Mark Esper, said Wednesday that should only be a "last resort."
New barriers were being erected outside the White House on Thursday as the protests for racial justice and police reform entered a 10th day.
Some of the protests were marred by rioting and looting in the early days but they have been mostly peaceful since then.
Curfews imposed in Los Angeles and Washington were lifted on Thursday.