Barack Obama last night (Tuesday) challenged America to do some "soul searching" about its treatment of impoverished black communities as troops and police flooded the streets of Baltimore to head off a second night of rioting.
At least 15 police were injured and 200 people were arrested overnight on Monday in violence caused by the death of Freddie Gray, a 25-year-old black man whose spine was severed after being arrested by Baltimore police.
Mr Obama condemned the "senseless violence and destruction" and added that his country was facing a crisis as police forces and black communities confronted each other in cities across the US.
"I think there are police departments that have to do some soul searching. I think there are some communities that have to do some soul searching. But I think we, as a country, have to do some soul searching," Mr Obama said.
As he spoke at the White House, police officers in riot gear and National Guard troops were readying themselves in Baltimore for another night of unrest.
The violence began on Monday afternoon after a post on a social media website called for a "purge" by young people against the police. The post was a reference to the 2013 horror film The Purge, which portrays the complete collapse of society.
By early evening, looting and disorder had spread across the western half of Baltimore and authorities declared a state of emergency.
Gangs of youths in hoods and masks raced through the streets in the back of pick-up trucks and at least one rioter used a knife to slash through a hose as the fire brigade struggled to contain a burning pharmacy. At least 15 buildings and 144 vehicles had been set on fire, according to the mayor's office.
Larry Hogan, the governor of Maryland, mobilised 500 National Guard troops and pledged to put "as much manpower" on the streets as possible.
"We're not going to have another repeat of what happened last night," he said.
Some citizens said they had lost faith in the authorities' ability to protect the public and were taking matters into their own hands. Brian Woodyard Jr stood outside a bar where he worked with a machete in his hand to deter looters. "Forget the law when the law can't protect civilians. This is kind of all-out war," he said.
The rioting came after several days of peaceful protest following the death of Mr Gray earlier this month. The FBI is investigating his death and six Baltimore officers have been suspended.
While many in Baltimore condemned the violence, saying it was only hurting an impoverished community, others said it was the only option for marginalised people. "I'm not condoning what's happening but I'm not condemning it either," said Dante Valentine as he watched a building burn. "No one has ever listened to peaceful protests so maybe this will get their attention."
Volunteers took to the streets yesterday morning to try to clear up some of the debris from the rioting. "This is our community and we've got to build it up," said Chavez Figgs, 18, as he swept up broken glass.