Some demonstrators hurled rocks at police as others scattered, while smoke engulfed the area. Two young men were seen preparing what looked like petrol bombs in a bus-stop shelter, their faces covered by bandanas. Police said protesters had thrown petrol bombs at officers.
Protesters have gathered every night since Saturday when 18-year-old Michael Brown was shot to death in the mostly black suburb of St Louis, during what authorities said was a struggle over a gun in a police car. Some witnesses say he was outside the car with his hands up.
Police have deployed camouflage-clad officers in body armour, including one manning a rifle on top of an armoured car.
President Barack Obama has called for a peaceful response to the shooting.