Demonstrators were held for unlawful assembly after staging a sit-in outside a convenience store early on Sunday, October 12.
Thousands of people in Missouri have taken part in rallies and vigils as part of a four-day event named Ferguson October.
Weeks of protests have been sparked by the killing of unarmed black teenager Michael Brown in nearby Ferguson.
Several demonstrators gathered outside a QuikTrip petrol station and convenience store in St Louis on Sunday morning, refusing to disperse.
Riot police used pepper spray to clear the protest.
St Louis police chief Sam Dotson said on his Twitter account that the protesters were “attempting to storm” the store and had thrown rocks at police officers.
Protesters denied throwing rocks at the police.
A QuikTrip store in Ferguson was wrecked during violent protests in the aftermath of Michael Brown’s killing, and later became a gathering point for protesters.
Tensions in St Louis are also high after another black teenager, Vonderrit D. Myers, was shot dead by a police officer on Wednesday.
Police said 18-year-old Vonderrit D. Myers shot at an officer, but the victim’s parents say he was unarmed and racially profiled.
Ferguson October began on Friday, October 10, when hundreds of demonstrators lined up outside the office of the local prosecutor, Robert McCulloch.
Demonstrators chanted slogans calling for Robert McCulloch to charge Darren Wilson, the officer who shot Michael Brown in August.
On October 11, there was a peaceful march through the centre of St Louis to the Keiner Plaza park. The crowd was larger than the day before, according to the Associated Press.
“This isn’t going to stop until there is change with police and black youth,” Tory Russell, one of the protest organizers, said.
Protest organizers said the weekend of events was intended “to build momentum for a nationwide movement against police violence”.
“We are here to bring peace, to bring restoration, to lift our banners in the name of those who’ve been sacrificed,” said another protest organizer, Montague Simmons.
Planned events include street protests as well as a music event and a day of “civil disobedience”.
Organizers have urged people from across the US to attend.
A US justice department investigation into the shooting of Michael Brown in August is continuing.
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