US President Joe Biden says the conviction of former police officer Derek Chauvin in the killing of George Floyd “can be a giant step forward” for the nation in the fight against systemic racism.

Mr Biden spoke from the White House on Tuesday (local time), hours after the verdict, alongside Vice-President Kamala Harris, with the pair calling for Congress to act swiftly to address policing reform.

“It’s not enough,” Mr Biden said of the verdict. “We can’t stop here.”

Mr Biden said Mr Floyd’s death was “a murder in the full light of day and it ripped the blinders off” for all the world to see the problems with race and policing in the US.

He said it was important to ensure black and brown people did not fear interaction with law enforcement.

Mr Biden spoke after telephoning Mr Floyd’s family just minutes after the unanimous jury verdict was handed down, telling them, “We’re all so relieved.”

Ms Harris, who spoke before Mr Biden, said the US still must work to reform the criminal justice system.

“A measure of justice isn’t the same as equal justice,” she said.

Tweet from @AttorneyCrump

Hours earlier, a crowd gathered outside the Minneapolis court erupted in cheers when the jury returned its verdict against Chauvin after just 10 hours of deliberation.

Chauvin, who faces up to 40 years in jail, was found guilty of second-degree unintentional murder, third-degree “depraved mind” murder and second-degree manslaughter in the death of Mr Floyd, a black man. Video of the incident touched off global protests over race and police brutality.

The 12 sequestered jurors considered three weeks of testimony from 45 witnesses, including bystanders, police officials and medical experts along with hours of video evidence.

Chauvin will be sentenced in eight weeks but is widely expected to appeal his conviction.

Tweet from @POTUS

Former US president Barack Obama also welcomed the conviction, saying it was the right decision but only one step in the fight for justice.

He said in a statement that true justice required Americans to understand that “black Americans are being treated differently every day” and that millions lived in fear that their next encounter with law enforcement could be their last.

Mr Obama said the country US needed to follow up on the verdict by taking concrete steps to reduce racial bias in the criminal justice system and to redouble efforts to expand economic opportunity in marginalised communities.

Politicians from both US parties expressed satisfaction with the guilty verdict.

California Democratic Representative Maxine Waters said: “I’m not celebrating, I’m relieved.”

South Carolina Senator Tim Scott, the chamber’s only black Republican, said he was thankful for a verdict that showed “our justice system continues to become more just”.

House Speaker Nancy Pelosi thanked Mr Floyd “for sacrificing your life for justice”.

Senate Majority Leader Chuck Schumer said Congress must keep working on legislation “to bring meaningful change” to police departments.

Meanwhile, legal experts say Chauvin will likely seek to overturn his convictions by arguing the jury was prejudiced by media coverage and a settlement in the civil case brought by Mr Floyd’s family, though his odds of success are slim.

Chauvin’s lawyers must notify the trial court within 60 days if they plan to appeal. His lawyers then have months to review transcripts and court filings to build their arguments.

Two weeks before trial testimony began, Minneapolis agreed to pay $US27 million ($A35 million) to settle a civil lawsuit brought by Mr Floyd’s family over his death.

The agreement was reached while jury selection in the criminal case was under way. Chauvin’s lawyer Eric Nelson said the settlement had an “incredible propensity to taint a jury pool”.

Judge Peter Cahill on March 19 rejected Mr Nelson’s request to delay the trial because of the settlement, a decision the defence is likely to raise on appeal.

Chauvin’s lawyers may also cite Judge Cahill’s decision to hold the trial in Minneapolis.

The defence had argued it was impossible to find an impartial jury in the city, which was rocked by protests over Mr Floyd’s death. But the judge said the case was one of the most scrutinised in history and moving it would make little difference.

Legal experts said there was little precedent for challenging a case based on venue and trials were rarely moved in Minnesota.

Another potential point of appeal could be media coverage and protests over a fatal police shooting in a nearby Minneapolis suburb late in the Chauvin trial

Police shot and killed black motorist Daunte Wright in Brooklyn Centre, Minnesota. US Representative Maxine Waters was in Brooklyn Centre at the weekend and urged protesters “to get more confrontational” if Chauvin was found not guilty.

That prompted Judge Cahill on Monday to call her comments “abhorrent”, though he also denied a request by Mr Nelson to declare a mistrial.

Joseph Friedberg, a Minnesota criminal defence lawyer, said an appeals court would not overturn a conviction because of media coverage or emotional protests.

“Cases aren’t going to be reversed on that basis,” he said.

-with AAP