A tanker truck has driven into a throng of protesters on a closed highway near Minneapolis, with the driver pulled from his rig and beaten by the demonstrators.
It comes as major US cities imposed curfews in fear of another night of demonstrations against police brutality descending into violence.
Commissioner of the Department of Public Safety John Harrington said the truck “literally drove” into a group of about 6000 demonstrators.
“In the midst of that crowd, the truck drove through at high speeds, was chased down by protesters and the truck stopped. The driver was taken out of the truck by the protesters and he was then taken to a medical centre,” he said.
The tanker truck driver is in custody and Minnesota state patrol is investigating whether charges should be laid.
But it did not appear any marchers were struck by the tanker as it sped through the crowd on the westbound lanes of Interstate 35 on Sunday, honking. The freeway was closed to traffic at the time.
“Very disturbing actions by a truck driver on I-35W, inciting a crowd of peaceful demonstrators,” the Minneapolis Department of Public Safety said on Twitter.
“The truck driver was injured & taken to a hospital with non-life threatening injuries. He is under arrest. It doesn’t appear any protesters were hit by the truck.”
The incident marked the latest outburst of violence following what began as peaceful demonstrations over the death of George Floyd.
At least 25 major US cities were bracing for a sixth night of violent protests on Monday (Australian time) over the death of Mr Floyd while being arrested.
The National Guard was being deployed in 15 states as streets across the country remained strewn with broken glass and burned-out cars.
In Minneapolis, where Mr Floyd’s arrest a week ago ignited the anger, 11,000 troops have been deployed to manage curfews and quell the protests.
There are widespread curfews across the US, but they have been ignored or have otherwise failed to stop confrontations between activists and law enforcement.
As night fell in Washington DC (Australian time), protesters gathered at the White House, where troops stood guard behind barricades.
Thousands of people gathered on Sunday for a rally in Minnesota’s twin city, St Paul, as state troopers surrounded the state capitol building after 170 stores were looted and many burned to the ground.
What began as peaceful demonstrations over the death of Mr Floyd, 46, last week as a white Minneapolis police officer knelt on his neck, have become a wave of outrage sweeping a politically and racially divided nation.
Video shot by bystanders showed Mr Floyd handcuffed, face-down on the road and one officer, Derek Chauvin, kneeling on his neck for almost nine minutes.
Mr Chauvin was arrested and charged on Friday with third-degree murder and second-degree manslaughter.
Curfews in Minnesota and St Paul will be enforced from 8pm to 6am, as authorities plead with citizens to “stay home” during “this very troubling time”. Tensions are expected to increase as night falls.
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 protesters who were pelting it with debris.
Mr 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 already killed more than 100,000 Americans.
Violence spread despite curfews in several major cities rocked by civil unrest in recent days, including Atlanta, Los Angeles, Philadelphia, Denver, Cincinnati, Portland, and Louisville.
“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.
On Sunday, Mr Trump said the US government would designate anti-fascist group Antifa as a terrorist organisation. It was not clear how many, if any, of the demonstrators are from Antifa.
Mr Chauvin’s arrest on Friday has failed to satisfy protesters. Three officers who stood by as Mr Floyd died have yet to be charged.