A rioter screams from atop a burning car during clashes in Baltimore, Maryland April 27, 2015.Reuters 
A man with looted goods walks by burned vehicles in Baltimore, Maryland April 27, 2015.Reuters 
A Baltimore Metropolitan Police transport vehicle burns during clashes in Baltimore, Maryland April 27, 2015.Reuters
Baltimore erupted in deadly riots on Monday as gangs, mainly of 'high school students', engaged in vandalism and looting, after a funeral service for Freddie Gray who died in police custody.
The Baltimore police commissioner said several "youthful residents" were behind the riots that left at least 15 police officers injured and led to a state of emergency being declared on Monday night.
SEE PHOTOS of the deadly Baltimore riots
"These are Baltimore youthful residents, a number of them came right out of the local high schools there on the other side of Mondawmin and started engaging in this," Commissioner Anthony Batts said, according to CBS Baltimore.
"And if you saw in one scene, you had one a mother who grabbed their child who had a hood on his head and she started smacking him on the head because she was so embarrassed. I wish I had more parents who took charge of their kids tonight," he added.
The riots may have been sparked by suspected flier on social media that called on high school students to participate in a rally.
Teenaged assailants took to hurling stones at police officials and their vehicles, and torched buildings and vehicles.
Governor of Maryland Larry Hagan has said he has called on the National Guard troops as a "last resort."
About 5,000 troops may be deployed in Baltimore.
The role of gangs running in Baltimore, such as the Black Guerilla Family, Bloods and Crips, have posed a "credible threat", the police said in a media statement.
The riots are reminiscent of unrest in Ferguson and other parts of the country in recent months over police brutalities and killings of members of the African-American community.
Gray, 25, died on 19 April a week after he was taken into police custody, with speculations that he died from injuries he sustained while being transported in a metal box in the back of a police wagon.
Video footages have shown that Gray was not strapped in when he was placed in the metal box, as is the norm, according to The Independent.
Gray's funeral service was held at a Baptist church in Baltimore on Monday.
