Baltimore Mayor Stephanie Rawlings-Blake called Monday night (27 April) one of her city's "darkest days" as protesters marched the streets and some she called "a small group of criminals" looted stores and set fire to buildings and cars.

Blake said Maryland Governor Larry Hogan has promised to send National Guard troops to help restore peace, and she ordered a week-long night-time curfew for all residents from 10pm to 5am beginning 28 April.

The violence broke out just a few blocks from the funeral of 25-year-old Freddie Gray, who died after a week in a coma from injuries sustained in police custody. Trouble then spread through parts of the city in the most violent US demonstrations since looting in Ferguson, Missouri, last year.

After more than an hour of mayhem, hundreds of police moved into glass-strewn streets where the worst of the violence had taken place and used pepper spray on rioters who had sacked convenience stores.

"This is one of our darkest days as a city and I know that we're much better than this," Blake told a group of reporters on Monday night. "We cannot allow our city to devolve into chaos because of a small group of criminals that are moving throughout our city."

Police and news helicopters buzzed overhead and older community leaders tried to calm down mostly young rioters and prevent clashes with the police. Rioters cut a fire department hose while firefighters fought a blaze at a CVS pharmacy looted earlier, police said.

Gray's death from spinal injuries on 19 April reignited a public outcry over police treatment of African Americans that flared last year after the killings of unarmed black men in Ferguson, New York City and elsewhere.

Officials have suspended six police officers who were involved in the case.