What began as peaceful demonstrations over the death of Floyd, who died as a white Minneapolis police officer knelt on his neck, have become a wave of outrage sweeping a politically and racially divided nation.

Protesters have flooded streets after weeks of lockdowns during the coronavirus pandemic that threw millions out of work and hit minority communities especially hard.

As demonstrators broke windows and set fires, police fired rubber bullets and tear gas to disperse crowds in many cities. In some cases, bystanders and members of the media were targeted.

In one video from Minneapolis, a National Guard Humvee rolls down a residential street followed by what appear to be police officers wearing tactical gear.

One officer orders residents to go inside, then yells “light ’em up” before shooting projectiles at a group of people on their front porch. The city’s curfew does not apply to residents outside on their private property.

In New York City, police arrested about 350 people overnight and 30 officers suffered minor injuries.

Mayor Bill de Blasio said police conduct was being investigated, including widely shared videos showing a police vehicle in Brooklyn lurching into a crowd of protesters who were pelting it with debris.

De Blasio said he had not seen a separate video showing an officer pulling down the mask of a black protester who had his hands in the air, then spraying a substance in his face.

The closely packed crowds and demonstrators not wearing masks sparked fears of a resurgence of COVID-19, which has killed more than 100,000 Americans.

Violence spread overnight despite curfews in several major cities rocked by civil unrest in recent days including Atlanta, Los Angeles, Philadelphia, Denver, Cincinnati, Portland, Oregon, and Louisville, Kentucky.

The clashes in Minneapolis marked the fifth night of arson, looting and vandalism in parts of the state’s largest city, and its adjacent capital, St. Paul. The state’s governor said on Saturday that he was activating the full Minnesota National Guard for the first time since World War II.

Thousands of people gathered on Sunday afternoon for a rally in St. Paul as state troopers surrounded the state capitol building.

About 170 stores have been looted and some burned to the ground in St Paul, its mayor said.

“We are seeing in St. Paul and obviously around the country this level of rage and anger that frankly is legitimate, as we see this horrific video of George Floyd being just suffocated to death,” Mayor Melvin Carter told CNN on Sunday.

“Unfortunately, it’s being expressed right now, over the past week, in ways that are destructive and unacceptable.”

The administration of President Donald Trump, who has called protesters “thugs”, will not federalise and take control of the National Guard for now, national security adviser Robert O’Brien said.

Trump said on Sunday that the US government will designate anti-fascist group Antifa as a terrorist organisation. It was not clear how many, if any, are from Antifa.

The arrest on murder charges on Friday of Derek Chauvin, the officer seen kneeling on Floyd’s neck, has failed to satisfy protesters. Three officers who stood by as Floyd died have yet to be charged.

Floyd’s name is only the latest to be chanted by protesters over the perceived lack of police accountability for encounters that resulted in the death of black men.

-AAP