The Missouri city erupted in street demonstrations after a court delivered a not guilty verdict to former St Louis police officer Jason Stockley in the 2011 killing of a black man following a high-speed chase.
More than 80 people have been arrested as protests in St Louis over the acquittal of a white policeman who had shot a black man turned violent for a third night running.
Police in riot gear used pepper spray and arrested demonstrators on Sunday night who had defied orders to disperse following a larger, peaceful protest.
After nightfall, a small group remained and the scene turned to one of disorder, following the pattern of Friday and Saturday. Protesters smashed windows and attempted to block a ramp to an interstate highway, police and witnesses said.
Officers tackled some protesters who defied police orders and used pepper spray before starting the mass arrests.
At a late-night news conference, Mayor Lyda Krewson noted that "the vast majority of protesters are non-violent," and blamed the trouble on "a group of agitators."
Acting police commissioner Lawrence O'Toole struck a hard stance saying, "We're in control, this is our city and we're going to protect it."
Acquitted of first-degree murder
The protests in St Louis followed the acquittal on Friday of former police officer Jason Stockley, 36, of first-degree murder in the 2011 shooting death of Anthony Lamar Smith, a 24-year-old black man.
The violence evoked memories of the riots following the 2014 shooting of a black teenager by a white officer in nearby Ferguson, Missouri.
Police reported confiscating weapons including handguns and recovered plastic spray bottles containing an unknown chemical that hit officers, who were then decontaminated.
"This is no longer a peaceful protest," St Louis police said on Twitter earlier.
Protesters broke large ceramic flowerpots and threw chunks of the ceramic at storefront windows.
Sunday's gathering was the largest of the three nights with more 1,000 protesters. Police, in turn, deployed their largest show of force, as officers in riot gear marched through the streets.
"Do they think this will make us feel safe?" said Keisha Lee of Ferguson, shaking her head.
The protests began on Friday shortly after the acquittal on Friday, when 33 people were arrested and 10 officers injured.
Violence flared anew on Saturday night when about 100 protesters, some holding bats or hammers, shattered windows and skirmished with police in riot gear, resulting in at least nine arrests. Sunday's arrests again followed earlier peaceful, and far larger, protests.
Black Lives Matter
More serious clashes broke out in 2014 in Ferguson, a suburb of St Louis, following the killing of 18-year-old Michael Brown by a white police officer who was not indicted.
The Ferguson protests gave rise to Black Lives Matter, a movement that has staged protests across the United States.
An informal group known as the Ferguson frontline has organised the protests, focusing on what it describes as institutional racism that has allowed police to be cleared of criminal wrongdoing in several shootings of unarmed black men.