Baltimore erupted in violence as hundreds of rioters looted stores, burned buildings and injured at least 15 police officers following the funeral of a black man who died in custody.
A state of emergency has been declared and the National Guard sent in as officials also ordered a week of overnight curfews in an effort to quell the disorder.
Violence broke out a short distance from the funeral of Freddie Gray before spreading through much of West Baltimore in the most violent US demonstrations since arson and gunfire in Ferguson, Missouri, last year.
Mr Gray's death had prompted several days of peaceful protests and Mayor Stephanie Rawlings-Blake said those involved in the lootings were "thugs" who had nothing to do with protests over police brutality.
"It's extremely heartbreaking for someone born and raised in Baltimore," she said.
"We know how hard people work to be able to have a city we know and love and watch a group of criminals go through our city with an intent to destroy. You don't get justice for that. What does it solve?"
Several blazes were sparked, including a fire that destroyed an old people's centre at a church in East Baltimore.
Police said at least 27 people were arrested as looting and attacks on officers continued into the night, and Baltimore schools will be shut on Tuesday. Liquor stores, pharmacies, a shopping mall and a cheque-cashing store were ransacked.
Rioters smashed car windows outside a major hotel and twice slashed a fire hose while firefighters fought a blaze at a CVS pharmacy that had been looted before it was set ablaze.
Mr Gray's death on 19 April revived public anger over police treatment of black Americans, which was sparked last year by the killings of unarmed black men in Ferguson, New York City and elsewhere.
Tony Luster, 40, who receives disability benefits and was out on the street watching the police line, said: "All this had to happen, people getting tired of the police killing the young black guys for no reason.
"It is a sad day but it had to happen."
A series of deadly confrontations between mostly white police and black men, and the violence it has prompted, will be among the challenges facing US Attorney General Loretta Lynch, who was sworn in on Monday.
