A protest over police use of force that started peacefully has grown increasingly chaotic with demonstrators breaking windows in central St. Louis in the US and others attempting to block a ramp to an interstate highway, police and witnesses say.
Police say they have an order for the crowd to disperse at one intersection after reports of significant property damage.
"Officers in personal protection gear have arrived on the scene in Downtown to disperse unruly crowd," St. Louis police said on Twitter on Sunday night.
Earlier in the evening, a handful of demonstrators threw bottles in response to a police officer making arrests, the first indication that the protest could turn violent as it did the previous two nights.
"Agitators are breaking multiple windows at Olive & 10th. Officers are heading to scene," St. Louis police said on Twitter.
"We have reports of significant property damage in Downtown #STL," said a second tweet.
The protests began after Circuit Judge Timothy Wilson on Friday acquitted former St. Louis police officer Jason Stockley, 36, of first-degree murder in the 2011 shooting death of Anthony Lamar Smith, 24.
Mr Stockley was recorded during the pursuit saying: "Gonna kill this [expletive], don't you know it."
Hundreds of protesters gathered for the third night in a row in the Missouri city of almost 320,000 people. The violence of the previous two nights evoked memories of the riots following the 2014 shooting of a black teenager by a white officer in nearby Ferguson, Missouri.