City leaders have appealed for calm in Milwaukee after violence erupted when police shot dead an armed man during a chase.
More than 100 protesters took to the streets of the city's north side on Saturday night after news of the shooting spread, erupting in clashes with police. Several businesses were also set alight and an officer was injured by a brick.
At a news conference later, Mayor Tom Barrett said the situation appeared to be calming after riotous scenes in which protesters skirmished with police, torching a squad car and throwing a brick through the window of another.
Police mounted at least two efforts to push the protesters from an intersection at the heart of the violence.
The unrest began several hours after the 23-year-old man trying to flee from police after a traffic stop was shot and killed.
Police said the man - who had a criminal record - was armed with a stolen handgun, but it was not clear whether he was pointing the gun or aiming it at officers.
Barrett said the man was hit twice, in the chest and arm. Neither his race nor the officer's was immediately released, nor were they identified.
The shooting was being investigated by the state. The officer was wearing a body camera, Barrett said.
At least three people were arrested in an uprising that Barrett said was driven by social media messages instructing people to congregate in the area.
"We have to have calm," Barrett said. "There are a lot of really good people who live in this neighbourhood."