Milwaukee leaders have pleaded for calm after violence erupted for several hours on the US city’s north side following a man’s fatal shooting by police.

At a news conference, mayor Tom Barrett said the situation appeared to be calming after a riotous scene in which as many as 100 protesters skirmished with police, torching a squad car and tossing a brick through the window of another.

The unrest began several hours after a man fleeing police after a traffic stop was shot and killed. Police said the man was armed, but it wasn’t 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 at the news conference. “There are a lot of really good people who live in this neighbourhood.”

An offer hides behind a car as the crowd erupts. Photo: AP

Milwaukee Common Council president Ashanti Hamilton echoed Barrett’s plea for help restoring order.

“We understand the frustration people feel with the police community nationally … We have to go through the process of finding justice, but we have to be able to restore order to these neighbourhoods,” Hamilton said.

Barrett said the 23-year-old man who died was stopped by police for “suspicious activity”.

Police said earlier that he was carrying a gun that had been stolen in a March burglary in suburban Waukesha.

“This stop took place because two officers … saw suspicious activity,” Barrett said. “There were 23 rounds in that gun that that officer was staring at. I want to make sure we don’t lose any police officers in this community, either.”

Police with shields and helmets moved slowly into an intersection after 1pm, telling a crowd of about 50 people to disperse. Some threw rocks and other debris at police, who held up their shields.

Police said the man who was shot had an arrest record. The 24-year-old officer who shot the man has been placed on administrative duty. The officer has been with the Milwaukee department six years, three as an officer.

-AP