Fires burned near the White House, stores were looted in New York City and Southern California, and a tanker truck drove into marchers in Minneapolis as the United States struggled to contain chaotic protests over race and policing.
National Guard troops were deployed in 15 states and Washington, DC in an attempt to quell a sixth night of violence on Sunday.
The unrest began with peaceful protests over the death of a black man, George Floyd, in police custody.
Video footage showed a white Minneapolis police officer kneeling on the neck of Floyd, 46, for nearly nine minutes before he died on May 25.
His death caused outrage across a nation that is politically and racially divided during a polarising presidential campaign, and has recently been released from strict stay-at-home orders during the coronavirus pandemic that threw millions out of work.
Authorities imposed curfews on dozens of cities across the US.
President Donald Trump described the protesters as "thugs".
"Get tough Democrat Mayors and Governors," Trump, a Republican, said on Twitter on Sunday afternoon. "These people are ANARCHISTS. Call in our National Guard NOW."
But Trump's administration will not take control of the National Guard for now, national security adviser Robert O'Brien said.
In Washington, DC, protesters set fires near the White House on Sunday. The smoke mixed with billowing clouds of tear gas as police sought to clear from the area crowds chanting "George Floyd".
Sporadic violence broke out in Boston following peaceful protests as activists threw bottles at police officers and set a police cruiser on fire. Philadelphia announced a 6pm to 6am curfew.
On Sunday afternoon, a tanker truck drove into demonstrators on the I-35 highway in Minneapolis, which had been closed to traffic.
The driver was pulled from the cab and beaten by protesters before police took him into custody. It did not appear any protesters were hit by the truck.
On the West Coast, there were also clashes in Portland, Oregon, where TV footage showed small fires burning as police fired tear gas at protesters who set off fireworks.
In Santa Monica, California, upscale stores were looted along the city's popular Third Street Promenade before police moved in to make arrests. The vandalism followed a largely peaceful march.
Further south, in the Los Angeles suburb of Long Beach, a group of young men and women smashed windows of a shopping mall and looted stores before they were dispersed before a 6pm curfew.
The demonstrations brought out a diversity of people.
"It means a lot to see people other than black people joining the demonstration," said Candace Collins, a young black woman at a march in Culver City, California.
Thousands of people gathered peacefully on Sunday afternoon for a rally in St. Paul, adjacent to Minneapolis, as state troopers surrounded the state capitol building. About 170 stores in the city have been looted, its mayor told CNN.
Protests spread around the globe, with events in London and Berlin on Sunday and others on Monday including in New Zealand, Australia and the Netherlands.
The eruptions of violence have not let up despite the arrest on Friday of former Minneapolis police officer, Derek Chauvin, 44. He has since been charged with third-degree murder.
In New York City, where store windows were smashed, police arrested about 350 people and 30 officers suffered minor injuries during clashes.
Mayor Bill de Blasio said police conduct was being investigated, with videos showing a police vehicle lurching into a crowd of protesters who were pelting it with debris in Brooklyn.
De Blasio said he had not seen a separate video showing an officer pulling down the mask of a black protester to spray something in his face.
Protests have also flared in Chicago, Seattle, Salt Lake City, Cleveland and Dallas, where rioters were seen on video beating a store owner who chased them with a large machete or sword. Police said on Sunday he was in stable condition.
Australian Associated Press