17 August 2014 Last updated at 07:37 BST
Police have fired multiple smoke canisters into a crowd of protesters in a St Louis suburb, where a black teenager was shot dead by a white officer last week.
Hundreds of other demonstrators left peacefully before a midnight curfew took effect.
But remaining protesters - chanting "no justice, no curfew" - refused to leave the area.
Corporal Juston Wheetley from the Missouri State Highway Patrol told the BBC: "We have no problem with them coming out and expressing their feelings... but we have to do it in a lawful manner."