Fresh protests broke out on Monday in Minneapolis despite a curfew implemented after a police officer fatally shot a young black man when she appeared to confuse her handgun with her taser, fueling tensions in a US city already on edge because of the George Floyd murder trial.

Nearly two hours after the curfew went into effect, dozens of protesters continued to wave signs and chant slogans in front of the police station in Brooklyn Center, where Sunday's killing occurred.

Demonstrators taunted police through newly-erected wire fencing around the station, and carried signs saying "Jail all racist killer cops", "Am I next?" and "No justice, no peace".

Police fired tear gas at the protesters several times and ordered them to disperse.

This was the second consecutive night of protests after 20-year-old Daunte Wright was shot dead by police while driving with his girlfriend.

In police body camera video released earlier on Monday, an officer shouts "Taser! Taser! Taser!" but then instead fires a gun at the victim.

"The officer drew their handgun instead of their taser," said Brooklyn Center police chief Tim Gannon, adding it was his belief the officer, now on leave pending an investigation, "had the intention to deploy their taser but instead shot Mr Wright with a single bullet".

How the officer mistook her gun for a taser was unclear.

Minnesota's Bureau of Criminal Apprehension identified the officer late on Monday as Kim Potter, a 26-year veteran of the police force.

Wright's killing sparked protests overnight in Brooklyn Center and the looting of a shopping mall. Authorities in Minneapolis and surrounding suburbs including Brooklyn Center announced a curfew from 7 pm on Monday until 6 am on Tuesday.

Biden warns against unrest

US President Joe Biden called the killing "tragic", but warned against any potential violent unrest. "I think we have to wait and see what the investigation shows," he said.

"In the meantime, I want to make it clear again: there is absolutely no justification, none, for looting. Peaceful protests－understandable."

The protests overnight prompted the defense attorney for former officer Derek Chauvin, who is facing murder and manslaughter charges for Floyd's death, to ask the judge presiding over the high-profile case to sequester the jury.

Judge Peter Cahill refused, stating "this is a totally different case".

Chauvin is facing murder and manslaughter charges for his role in Floyd's death on May 25, 2020, which occurred during his arrest for allegedly passing a fake $20 bill.

The 45-year-old Chauvin, who is white, was seen in a video taken by a bystander kneeling on Floyd's neck for more than nine minutes as the handcuffed 46-year-old black man complained repeatedly he could not breathe.

The video touched off protests against racial injustice and police brutality in the United States and around the world.

Also on Monday, police shot and killed a Knoxville, Tennessee, high school student after they said he opened fire on them in a campus bathroom, wounding an officer.

The gunfire, which erupted at about 3:15 pm at Austin-East Magnet High School on the east side of Knoxville, marked the latest in a rash of shootings in the US since mid-March.

Agencies and Ai Heping in New York contributed to this story.