About 40 people were arrested just north of Minneapolis in a second night of unrest over the police shooting of a black man.
Protesters in the city of Brooklyn Center defied a curfew and threw objects at police, who responded with flash grenades and tear gas.
Police said Daunte Wright, 20, was shot and died after an officer mistook her gun for a Taser during a traffic stop.
The shooting came as the high-profile George Floyd murder trial continues.
In a courtroom just a few miles away, ex-police officer Derek Chauvin is charged with murdering the African American man in May last year.
Derek Chauvin’s defence team on Monday asked for the jury members to be sequestered – separated from other people – as they might be swayed by the latest events. The judge denied the request.
The officer who shot Mr Wright was named on Monday as Kim Potter, 48, who has worked for Brooklyn Center Police for 26 years.
Mr Wright was pulled over on Sunday for a traffic violation, but there was a struggle when he tried to get back into his car.
After mistakenly drawing her gun, the officer said: “Holy shit, I just shot him.”
What happened overnight?
The curfew went into force at 19:00 (midnight GMT) across four counties with a huge law enforcement deployment.
In a press briefing after midnight local time, Minnesota State Patrol colonel, Matt Langer, said officers had reached out to organisers of protests to try to keep them peaceful but “unfortunately those efforts weren’t successful and the organisers weren’t able to influence the desires of the crowd”.
Col Langer said officers had been “shelled pretty significantly with objects” including fireworks.
He said protesters had pushed against the fence of the Brooklyn Center police headquarters and a decision had been made to push back the crowd.
There were “sporadic” incidents of looting in the area and in other parts of Minneapolis and neighbouring St Paul.
In response to the unrest, US President Joe Biden said peaceful protest was “understandable” but added: “I want to make it clear again: there is absolutely no justification, none, for looting.”
Shortly before midnight, Brooklyn Center Mayor Mike Elliot issued a positive tweet, saying: “Our city is calm now, thank you all who came out to peacefully protest then went home.”
What happened to Daunte Wright?
Police Chief Tim Gannon gave details of the police action after officers pulled Mr Wright over, saying he believed the shooting that followed to be “an accidental discharge”.
During a news conference on Monday, he played a short video from the body camera worn by the policewoman which shows Mr Wright trying to get back into his car as officers attempt to handcuff him on the side of the road.
An officer can then be heard saying “Taser, Taser, Taser” – normal police procedure before firing one of the stun guns. Mr Wright is seen to get into his car and drive away, while the same officer admits, using an expletive, to having shot him.
Fatally wounded, Mr Wright crashed a few streets away.
“It is my belief the officer meant to deploy their Taser but shot him with a single bullet,” Chief Gannon said, adding: “There’s nothing I can say to lessen the pain.”
The officer has been placed on administrative leave – temporary leave with benefits and salary still paid.
Mayor Elliot has said she should be fired. He will make a decision on Tuesday about whether Chief Gannon will keep his job, the StarTribune reported.
Why Minneapolis is tense
The trial of Derek Chauvin over the death of George Floyd has been under way in the city for two weeks now.
Mr Chauvin was filmed kneeling on Mr Floyd’s neck for more than nine minutes during an arrest operation in Minneapolis last May. The footage of the incident sparked global protests against racism.
On Monday, Mr Chauvin’s lawyer Eric Nelson called for jury members to be asked about the Daunte Wright shooting to determine if what they had heard could affect their verdict.
He repeated a call for the jury to be kept separate from the public, but Judge Peter Cahill said full sequestering would only start when closing arguments began.
Law enforcement officials have been bracing for possible unrest once the jury reaches a verdict.
George Floyd’s death sparked waves of protests around the city, many peaceful but some violent with hundreds of buildings damaged.
‘You took his life, for what?’
BBC’s Barbara Plett-Usher reports from the scene
One sign at the protest captured the mood: “During the trial!!?” it read in bright orange letters.
“It’s ridiculous,” said the young man carrying it. “They know they have a delicate relationship with the black community right now and they should look to be making amends, not this.”
City officials had said the shooting could not have happened at a worse time, with tensions high over the George Floyd case.
Some protesters threw bottles and shot fireworks toward police lines. They vented their rage as officers in riot gear stood impassively. “You took his life, for what?” screamed a young woman.
“He was a son, he was a father, he was a black man that deserved to live.”
“Do you know the difference between a gun and a Taser?” shouted someone else. “Hell yeah,” roared the crowd, scorning the police chief’s belief that the shooting was a tragic mistake.
“There’s no room for accidents,” said one man. “The fact is that we lost another young black male to a police officer.’