The loud crack of a gunshot startled protesters as they hurled objects and clashed with riot police in Charlotte, North Carolina, where racial tensions soared a day after a black man was killed by officers.
By the end of the day, Governor Pat McCrory had declared a state of emergency in the city, saying he was activating the National Guard and Highway Patrol officers to assist local law enforcement.
One man near the centre of yesterday's confrontation was on life support after being shot by another civilian, the city said in a tweet, reversing an earlier statement that the man had died.
The unrest turned violent after a peaceful vigil to mark the previous day's shooting death of African-American Keith Scott at the hands of Charlotte police.
It was the latest in a long series of controversial police killings of black men - including that of Terence Crutcher in Tulsa, Oklahoma, on Saturday - which have inflamed tensions in several United States cities, and sparked a national debate about race and whether Americans can come together to reduce police brutality.
The Charlotte protesters came face to face with helmeted security forces in riot gear, who massed uptown but were briefly outnumbered by the hundreds of demonstrators who took over the streets, kicking police vehicles and breaking storefront glass.
The police were forced to retreat to the safety of an upscale hotel lobby. Protesters tried to push their way inside but were blocked, and police eventually established a perimeter at the hotel's entrance.
When agitators got too close, or projectiles rained down, police used rubber bullets, pepper spray and flash grenades to disburse the crowd.
Some appeared undaunted, surging back toward the police.
"Your life is in danger, you need to move!" an officer yelled.
As the protest turned chaotic, a reporter heard the clear sound of a gunshot, which sent several people running.
The shooting victim fell to the sidewalk 2m from an AFP photographer, and riot police and other protesters helped move the injured man behind the police perimeter. A pool of blood was left on the sidewalk.
Yesterday's mayhem followed a dusk vigil for Scott, a 43-year-old father killed by police in a Charlotte apartment complex under disputed circumstances.
The police chief said Scott was holding a gun and posed a threat to officers, and that the policeman who shot him was black. But neighbours told a dramatically different story, saying Scott was reading a book, not holding a firearm, and that the officer who shot him was white.
"It's a lie," said Taheshia Williams, whose daughter attends school with the victim's son. "They took the book and replaced it with a gun."
Charlotte-Mecklenburg police chief Kerr Putney said: "He stepped out, posing a threat to the officers, and officer Brentley Vinson subsequently fired his weapon, striking the subject."
He added: "I can tell you a weapon was seized. A handgun. I can also tell you we did not find a book that has been made reference to."
While yesterday's vigil was peaceful - several attendees brought their children - the atmosphere changed dramatically once demonstrators walked to the nearby police headquarters, where one protester pulled the American flag to the bottom of its flagpole.
Other people banged angrily on the front doors and chanted "No justice, no peace," and "F*** the police."
By the time they walked the few blocks to uptown, and encountered riot police standing like statues, protesters were seething.
"It's too much. It's too much," winced one woman, wiping tears from her eyes as she stood before riot police.
"We've got brothers and sisters and children and fathers who think we're not going to live to see the next day. Nobody should have to live like that," she said. "Not every black person is a drug dealer, a crackhead, or a gangster."
Several protesters raised their arms as they stood before police, chanting "Hands up, don't shoot."
But while officials were eager to defuse the anger on the streets, many protesters were outraged that the police department has so far refused to release the body-cam and dashboard footage from the officers at the scene of Scott's death. One woman standing near the riot police held up a sign that read: "Release the Tapes."
In the southern state of Oklahoma, Tulsa police chief Chuck Jordan called video footage of deadly shooting on Saturday of Terence Crutcher disturbing and "very difficult to watch". The 40-year-old is seen with his hands up, appearing to comply with police officers before he is shot once by officer Betty Shelby and falls to the ground. Another officer fires his stun gun.
The US Department of Justice said on Tuesday it would conduct a federal civil rights probe into the Tulsa shooting, parallel to an investigation being carried out by local authorities.
Before yesterday's protest, presidential candidates Donald Trump and Hillary Clinton weighed in on the violence in Charlotte, which came on the heels of another fatal police shooting of a black man, Terence Crutcher, on Saturday in Tulsa.
"Keith Lamont Scott. Terence Crutcher. Too many others. This has got to end. -H," tweeted Democrat Clinton, signing the post herself.
After calling to "make America safe again" in a tweet, Trump suggested later yesterday that the Tulsa officer who shot Crutcher had "choked". "I don't know what she was thinking," the Republican said, speaking at an African-American church in Cleveland, Ohio.