Americans protest against killing of an African American by the white Minneapolis officer who pressed his knee into George Floyd’s neck amid his begging for air.

Thousands of protesters marched on Friday night through downtown Minneapolis, Minnesota’s largest city, defying an 8 pm curfew imposed by the mayor to try to stem the rallies.  

About 500 demonstrators clashed Friday evening with riot police outside the burned Third Precinct police station that protesters had set on fire the previous night.

Pain and anger over the death of Floyd has unleashed four nights of violent protests. The renewed protests come the same day Officer Derek Chauvin, 44, was charged with third-degree murder and second-degree manslaughter.

Officials had hoped Chauvin’s arrest would calm public anger and prevent continued civil unrest.

Large demonstrations were also held on Friday in several cities across the US, including New York, Atlanta, Detroit, Denver, Houston and Washington, DC.

Minneapolis community organizer Mike Griffin said the protests reflected years of frustration over economic inequalities and the feeling that black lives were not valued as highly by police.  

He said anger has been building since the 2015 fatal shooting by Minneapolis police of 24-year-old Jamar Clark, and the 2016 killing of Philando Castile, a 32-year old black man shot by Minnesota police during a traffic stop.

Minnesota Governor Tim Walz declared a state of emergency on Thursday and called in the state’s National Guard.

Floyd, 46, was arrested for allegedly using counterfeit money at a store to buy cigarettes on Monday evening.

Chauvin had his knee on Floyd’s neck for 8 minutes and 46 seconds, according to an autopsy report. Medical examiners found the combined impact of being restrained by police, underlying health conditions and any potential intoxicants in his system likely contributed to his death.

Chauvin, 44, was charged with third-degree murder and second-degree manslaughter. He faces up to 25 years in prison if convicted,

Floyd’s brutal killing was reminiscent of the killing of Eric Garner, an African-American who died in New York City in 2014 after being held in a chokehold by a white police officer, despite repeatedly telling officers, “I can’t breathe.”

Police-involved shootings and killings of unarmed black men in the hands of white police officers have led to mass protests across the US in recent years and the formation of the Black Lives Matter movement.