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 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 drawing her gun, apparently by mistake, the officer said: “Holy shit, I just shot him.”
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 to try to keep protests peaceful but “unfortunately… 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 said he had spoken to Daunte Wright’s father and would “do everything to ensure justice is served”.
Just got off the phone with Daunte’s father to offer my condolences. I cannot begin to imagine the pain his family is going through right now, but we grieve with you for your loss. I also assured him that I will do everything to ensure justice is served. pic.twitter.com/7D8JazK0dZ
— Mayor Mike Elliott (@mayor_elliott) April 12, 2021