Wisconsin Gov. Scott Walker has declared a State of Emergency for Milwaukee County and said the National Guard could step in "as the adjutant general deems necessary" following a night of protests that turned violent in response to a fatal police shooting of an armed African-American man.

Walker said he put the guard on alert following a request from Milwaukee County Sheriff David A. Clarke Jr. and after talking with Mayor Tom Barrett and Major Gen. Donald Dunbar.

A fire broke out at around 10:15 p.m. Central time on Saturday at a BP gas station, followed by more blazes at local businesses in the area, the Milwaukee Journal Sentinel reported. At 2:20 a.m. Sunday, Milwaukee police tweeted that they were restoring order to the area and were reducing deployments.

Sources have told the Journal Sentinel that the 24-year-old officer who shot the suspect is black. The slain suspect has been identified by family and police sources as 23-year-old Sylville Smith, who is also black.

There were 23 rounds in the Smith's gun, Barrett said. Smith was hit by the officer's gun once in the chest and once in the arm

Smith also had a "lengthy arrest record," police said, adding the handgun was taken in a March burglary in Waukesha. The owner reported that 500 rounds of ammunition also were stolen.

The officer involved was wearing a body camera during the incident and Barrett said he understands it was operational during the incident. He has since been put on administrative leave pending an investigation.

The violence came after a standoff between the Milwaukee Police Department and an angry crowd of protesters. During the course of the evening, Assistant Police Chief James Harpoon said there were multiple gunshots that prevented officials from properly handling the protests and containing the fires.

Sheriff Clarke said Sunday he would "not allow for a repeat of what happened last night."

Protests have been relatively quiet so far Sunday, including a gathering of a few hundred people near the BP gas station that was destroyed by fire the previous night. People were seen helping to clean up damage done the night before.

The officer-involved shooting took place following an on-foot pursuit of a suspect who took off on foot after being stopping in a car by Milwaukee police at about 3:30 p.m. local time Saturday afternoon.

During the pursuit, Mayor Barrett said, the suspect did not comply with the officer when asked to put his handgun down.

Alderman Khalif Rainey, who represents the area where the Smith was fatally shot, said the protests stem from the frustrations of black Milwaukeeans and the problems they face.

"This entire community has sat back and witnessed how Milwaukee, Wis., has become the worst place to live for African-Americans in the entire country," Rainey said at a news conference. "Now this is a warning cry. Where do we go from here? Where do we go as a community from here? Do we continue — continue with the inequities, the injustice, the unemployment, the under-education, that creates these byproducts that we see this evening? ... The black people of Milwaukee are tired. They're tired of living under this oppression."

Protests also followed the fatal police shootings of Jay Anderson in Wauwatosa in 2016 and Dontre Hamilton in Milwaukee in 2014.

The Milwaukee Police Association, the local police union, issued a statement Sunday defending the shooting and calling the unrest "terrorist-like."

"Our ranks are broad and diverse. ... These officers deserve respect and support ... which must begin with leadership," union President Mike Crivello said. He called the violent protestors "thugs" and "terrorists" and said they "must be held accountable."