Baltimore erupted in violence on Monday as hundreds of rioters looted stores, burned buildings and injured at least 15 police officers after the funeral of a 25-year-old black man who had died after he was injured in police custody.

The riots broke out just a few blocks from the funeral of Freddie Gray and then spread through much of west Baltimore in the most violent US demonstrations since those in Ferguson, Missouri, last year.

Maryland Governor Larry Hogan declared a state of emergency and called in the National Guard to restore order. US Attorney General Loretta Lynch, in her first day on the job, said she will send US Justice Department officials to the city in coming days.

At least 15 officers were hurt, and at least 27 people were arrested. Two officers remained hospitalized, police said.

Baltimore Mayor Stephanie Rawlings-Blake imposed a citywide curfew for adults beginning on Tuesday night from 10 pm to 5 am, with exceptions for work and medical emergencies.

Gray was arrested on April 12 when he fled from police in a high-crime area. Gray, who had been carrying a switchblade knife, was put inside a transport van to be taken to a police station.

At some point, Gray suffered the spinal injury that led to his death a week later. City Police Commissioner Anthony Batts said on Friday that officers had failed to belt him into his seat securely and to give him timely medical attention.

On Monday, Baltimore police used pepper spray on rioters who had sacked check-cashing and liquor stores. Looting spread to a nearby shopping mall, and rioters smashed car windows outside a major hotel.

Rioters twice slashed a fire hose while firefighters fought a blaze at a CVS Pharmacy drugstore that had been looted before it was set on fire.

Reuters - AP