More than 1,000 Maryland police officers, the Maryland National Guard, and 5,000 officers from neighboring states are on standby in the city and the Obama has been briefed on the situation as violence continues to escalate.

It is the same level of reinforcement the city requested during the riots of 1968 after Martin Luther King Jr was assassinated.

The scenes of destruction were initially billed as anti-police protests to avenge the death of Freddie Gray, who suffered a fatal spinal cord injury in police custody on April 12. But it rapidly mushroomed into uncontrolled riots.

Fifteen police officers have been injured, many suffering broken bones, and at least one appeared 'unresponsive'. Two of the 15 are in hospital in a serious condition. At least 27 people have been arrested.

Rioters continued to loot gun stores, check cashing stores, liquor stores and supermarkets well into Tuesday morning. Balaclava-clad mobs were seen ripping the doors off one rifle shop and passing weapons to people on the streets.

Death of Freddie Gray, an African American man who died of spinal cord injuries in police custody, in Baltimore, Maryland, April 25, 2015 make another angry demonstration against racism in US.