Police dressed in riot gear moved in on the Sherman Park neighborhood around 11:00 PM yesterday (0930 IST today) to disperse an angry crowd and restore order.
Several police officers have been targeted and shot dead across the nation in recent weeks - including five in Dallas - following an outcry over the deaths of unarmed African Americans at the hands of police.
In Milwaukee, in the Midwest state of Wisconsin, officers at one point used an armored vehicle to rescue a shooting victim and rush the person to hospital.
An unspecified "projectile" was thrown at another officer, who was protected by a helmet.
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One squad car was damaged by thrown bricks, rocks and glass bottles.
"Officers continue to have rocks thrown at them as they work to disburse small, disorderly groups in area around Sherman and Burleigh," police said on Twitter, adding that armored vehicles were deployed to protect officers.
"Multiple" arrests were made, it said.
Some 125 members of the Wisconsin National Guard were activated and placed on standby early yesterday to prevent a repeat of the arson, rock-throwing and shootings that occurred the previous night.
On Saturday, an angry crowd of at least 200 people took to the streets, torching at least six businesses, including a BP gas station and auto parts store that were destroyed, police said.
Individuals attending the rally fired dozens of shots, apparently in the air.
Violence broke out following the fatal shooting of local man Sylville Smith, 23.
Even though Smith was said to be armed and had a lengthy police record, the shooting and its aftermath bore chilling echoes of a series of violent incidents involving law enforcement.