The US town of Ferguson has seen rioting and looting after a jurydecided not to bring charges over the killing of a black teenager.
Michael Brown was shot by a white police officer, Darren Wilson, on 9 August, sparking protests.
A police chief said violence in the suburb of St Louis, Missouri, was "probably much worse" than on any night since the teenager's death.
St Louis County police chief Jon Belmar said rioters had fired 150 shots.
Many in the African-American community had called for Mr Wilson to be charged with murder, but following lengthy deliberations a Missouri grand jury - of nine white and three black members - made no recommendation of charges.
President Barack Obama joined the teenager's family on Monday in appealing for calm, urging Americans to accept the decision was "the grand jury's to make''.
The BBC's Aleem Maqbool reported seeing more vandalism and looting after Monday's ruling than on any night in August.