Protesters have streamed into the streets of St Louis after a white former police officer was found not guilty of murdering a black man in a 2011 shooting.
Officers had been on standby in case of violence and authorities appealed to protesters to march peacefully, but police said the protest was no longer peaceful and asked demonstrators to leave the area.
About 50 riot police monitored hundreds of demonstrators as they marched one block away from the courthouse.
Protesters had surrounded a police vehicle in front of the old police building near Tucker Boulevard and Clark Avenue and were damaging it with rocks.
Police approached and tried to secure the vehicle and protesters threw rocks and pieces of curbing at them.
Police then used pepper spray on the protesters.
It came after a judge acquitted Jason Stockley of first-degree murder for killing Anthony Lamar Smith.
The 36-year-old was arrested in May 2016 and accused of planting a gun in Smith’s car, but he said he had acted in self-defence.
After the verdict, the protesters chanted “no justice, no peace” and “shut it down”, while some held Black Lives Matter signs.
Reverend Clinton Stancil of the Wayman AME Church in St Louis, said: “I’m sad, I’m hurt, I’m mad. We haven’t made any progress since Ferguson, that’s clear. Cops can still kill us with impunity.”
Mayor Lyda Krewson and Governor Eric Greitens, who put the National Guard on standby, appealed for calm as schools and businesses in the area closed early.
In a statement, the mayor said: “Frustration, anger, hurt, pain, hope and love all intermingle. I encourage St Louisans to show each other compassion.”
Al Watkins, an attorney for Smith’s fiancee, Christina Wilson, said his client was appalled by the decision.
He said the ruling showed prejudice, pointing to a line where the judge wrote that an “urban heroin dealer” without a weapon would be an anomaly.
Judge Timothy Wilson’s ruling was announced more than five weeks after the bench trial ended.
He wrote in his ruling: “This court, as a trier of fact, is simply not firmly convinced of defendant’s guilt.”
Prosecutors also asked the court to consider a lesser degree of homicide, but they were unable to prove beyond a reasonable doubt that Stockley’s use of deadly force was not justified in self-defence.
Stockley’s attorney was not available for comment.