Demonstrators in Ferguson, Missouri chanted “Hands up, don’t shoot.”
Police fired tear gas after a violent minority disrupted the latest mostly peaceful protests after black teenager Michael Brown was shot dead by a white police officer in the St. Louis suburb on August 9.
Riot police took two guns and a petrol bomb from protesters on Monday night.
“I want to encourage the good people of this area to come out and protest during the daytime hours,” said Captain Ron Johnson, Missouri Highway Patrol, addressing a news briefing.
“Make your voices heard when you can be seen and when you’re not the cover for violent agitators,” he suggested.
President Barack Obama and civil rights leaders have appealed for calm while a federal investigation into the shooting proceeds.
Brown was shot dead by 28-year-old police officer Darren Wilson, who is now on paid leave, in hiding and under criminal investigation.
Police chiefs have yet to explain why Wilson fired multiple rounds at the unarmed teenager.