A US former police officer on trial for the death of a young African-American man wept in court Friday as she described how a routine traffic stop descended swiftly into chaos.

Kim Potter, 49, is charged with first-degree manslaughter over the fatal shooting of Daunte Wright, 20, in Brooklyn Center, a suburb of Minneapolis, Minnesota, in April this year.

She claims the shooting was an accident, saying she mistakenly grabbed her gun instead of her Taser.

"We were struggling, we were trying to keep them from driving away. And then it just went chaotic, I remember yelling 'Taser Taser Taser.' And nothing happens, then he told me I shot him," Potter said, bursting into tears.

She said the moments that followed were largely a blank. 

"They have an ambulance for me and I don't know why. And then I went, then I was at the station. I don't remember a lot of things afterwards," she said. 

On Sunday, April 11, 2021, the white policewoman was patrolling with a colleague who decided to look up the driver of a white Buick that had committed a minor traffic violation. 

After realizing that the driver was the subject of an arrest warrant, the police officers decided to arrest him. Potter described that as a potentially dangerous situation.

"Sometimes there's guns in the car. Sometimes there's uncooperative people, you don't know who you're stopping," she told the court.

Wright, who was unarmed, resisted being handcuffed and restarted his car to try to flee. Potter then drew what she said she thought was her Taser. 

On a recording of the scene, Potter can be heard shouting "Taser" several times, before shooting with her gun and fatally wounding Wright. 

The incident came during the trial of white policeman Derek Chauvin who had asphyxiated George Floyd in Minneapolis in May 2020 by kneeling on his neck for some nine minutes.

Floyd's death sparked nationwide protests against racism and police brutality. 

Wright's death also triggered several nights of protests and unrest in Brooklyn Center before Potter's own arrest calmed tensions.

Potter's lawyer, Paul Engh, argued that Wright's death was a result of human error and the stress that his client was under, maintaining that she was attempting to protect a fellow officer as Wright tried to drive off. 

But for prosecutor Erin Eldridge, Wright died because of Potter's reckless handling of her weapon and the negligence of an officer with 26 years on the force.

Ben Crump, the lawyer for Wright's family, said in a statement that Potter's testimony showed that "Daunte Wright's killing at Potter's hands was absolutely preventable."