Maryland Governor Larry Hogan Monday declared a state of emergency in Baltimore as violent protests and arson erupted across the eastern port city, according to dpa. Hogan Tweeted news of the emergency order which follows a week of protests over the recent death of a young black man, Freddie Gray, in police custody. There were several dozen arrests over the weekend, but the violence was nothing like that on Monday, when teenagers burst out of school, throwing rocks at police, looting and setting fire to stores and destroying cars. The Baltimore Sun reported that students were following a social media flier about a "purge" that was to take place after school starting at Mondawmin Mall in Baltimore and ending downtown. The message was a reference to the film, The Purge, about a 12-hour suspension of all criminal laws. Billie Murphy, an attorney for the family of Freddie Gray said that the rioters were teenagers. Reverend Jamal Bryant, who delivered Gray's funeral eulogy earlier in the day, said he was trying to convince "these black children on the streets" to go home. Baltimore Police also tweeted, "we are asking for PARENTS to please bring your children home. We don't want to see anyone get hurt." Police in riot gear formed cordons to protect themselves, according to broadcast TV images. But they did not intervene in the looting of a CVS pharmacy store until it was set on fire. After firefighters arrived to quell the smoke, rioters cut holes in the hoses to reduce the water flow. Seven Baltimore police officers were injured by rocks and other projectiles, police spokesman Eric Kowalczyk said. The injuries included broken bones and one office was unresponsive. "This is a group of lawless individuals with no regard for the safety of people who live in that community," Kowalczyk said. The riots forced the Baltimore Orioles baseball team to postpone, if not cancel, a night game as protestors moved from west Baltimore into the city center. Police fired paint ball guns at protestors who threw projectiles, and threatened to use tear gas and pepper shot. Earlier Monday, Baltimore police said they had received "credible information" that violent gangs planned to kill law enforcement officers as retaliation over Gray's death. "This is a credible threat," the Baltimore Police Department warned. The statement said that the police intelligence unit had learned that members of various gangs had "formed a partnership to 'take out' law enforcement officers." The gangs included the Black Guerilla Family, Bloods and Crips. Gray, 25, was arrested April 12 and died April 19 in hospital after falling into a coma. A post-mortem exam showed that Gray's death was the result of a spinal cord injury, police said. The incident follows rounds of nationwide demonstrations after a series of deaths of African-American suspects while confronting police or in police custody in the US since August. Baltimore police say Gray was pursued because he "fled unprovoked upon noticing police presence." After capturing him, police took him into custody on a weapons charge. Citizen videos showed the handcuffed Gray seemingly unable to stand as he is dragged by officers to a police van. The US Justice Department has opened an investigation into the circumstances that led to Gray's death. Earnest said he was confident the probe will "run its usual course."