Tensions between the demonstrators and police quickly escalatedThe US state of Missouri is sending the National Guard to the town of Ferguson as protests escalate over the police shooting of an unarmed black teenager.
Governor Jay Nixon signed an order to "help restore peace and order and to protect the citizens of Ferguson".
The move came as police clashed with angry demonstrators shortly before a second night under curfew began.
Officers eventually dispersed the crowds and no incidents were reported during the curfew, which has now ended.
Earlier, police in Ferguson, a suburb of St Louis, said they came under attack and had "no alternative" but to respond.
Capt Ron Johnson said protesters had shot at officers and thrown petrol bombs and bottles before the five-hour curfew started at midnight local time (05:00 GMT).
He described the violence as "premeditated criminal acts" to provoke a reaction. A number of people were injured during the unrest, and police made several arrests.
Missouri declared a state of emergency and imposed a curfew on Saturday in response to the escalating violence.