Updated 11.06pm Tuesday

A former Minneapolis police officer has been convicted of the murder of George Floyd last year in a case which sparked violent protests across the United States.

After deliberating for 11 hours, the jury in "Minnesota vs Derek Chauvin" reconvened at 10.30pm (Malta time) on Tuesday and declared Chauvin guilty on all counts. A large crowd outside the fortified courthouse greeted the verdict with cheers and applause. 

Chauvin, 45, who is white, was captured on video kneeling on Floyd's neck for more than nine minutes as the handcuffed 46-year-old Black man said repeatedly "I can't breathe."

Sentencing is expected in a matter of weeks. The former officer faces a maximum jail term of 40 years but experts expect a lower sentence since Chauvin has no previous convictions. Bail was revoked.

The Floyd family lawyer hailed the verdict as a 'turning point in history'.

White House spokeswoman Jen Psaki said President Joe Biden had spoken with Floyd's family on Monday to "check in with them and also share that the family was in his prayers."

Prosecutors and the defence presented their closing arguments on Monday and Judge Peter Cahill sent the case to the seven-woman five-man jury.

In his final instructions to the jury, the judge noted the gravity of the case, which comes amid heightened tensions fuelled by other police killings. 

"You must not let bias, prejudice, passion, sympathy or public opinion influence your decision," Cahill said. "You must not consider any consequences or penalties that might follow from your verdict."

Philonise Floyd (C), brother of George Floyd, arrives at the Hennepin County Government Center in Minneapolis, Minnesota.

The jury had to return a unanimous verdict.

Three other former police officers involved in Floyd's arrest for allegedly passing a counterfeit $20 bill are to go on trial later this year.

- National Guard deployed -

Amid fears of potential unrest, National Guard troops have been deployed in Minneapolis and Washington, the nation's capital.

Minneapolis has been the scene of nightly protests since Daunte Wright, a 20-year-old Black man, was shot dead in a suburb of the Minnesota city on April 11 by a white policewoman.

Some 400 protesters marched through the city on Monday calling for Chauvin's conviction, chanting: "The world is watching, we are watching, do the right thing."

In Washington, the National Guard said some 250 troops were being deployed "to support local law enforcement" in response to potential demonstrations.

Prosecutors, in closing arguments on Monday, showed excerpts from the harrowing bystander video of Floyd's death that was seen by millions around the world.

"This case is exactly what you thought when you saw it first, when you saw that video," prosecutor Steve Schleicher told the jury. 

"You can believe your eyes," Schleicher said. "It's exactly what you knew, it's what you felt in your gut, it's what you now know in your heart."

"This wasn't policing, this was murder," Schleicher said. "Nine minutes and 29 seconds of shocking abuse of authority."

Defence attorney Eric Nelson told the jury they need to look at Chauvin's actions "from the perspective of a reasonable police officer."

"He did not purposefully use unlawful force," Nelson said.

He said Floyd's heart disease and drug use were factors in his death and "the state has failed to prove its case beyond a reasonable doubt."

Much of the three-week trial involved testimony from medical experts about Floyd's cause of death.

Medical experts for the prosecution said Floyd died from a lack of oxygen from Chauvin's knee on his neck and that drugs were not a factor.

The defence called a retired police officer who said Chauvin's use of force against Floyd was "justified."

Police officers testifying for the prosecution -- including the Minneapolis police chief -- said it was excessive and unnecessary.