Two cars burn in the middle of an intersection at New Shiloh Baptist Church on April 27, 2015 in Baltimore, Maryland. Riots have erupted in Baltimore following the funeral service for Freddie Gray, who died last week while in Baltimore Police custody. Andrew Burton/Getty Images

Baltimore officials lashed out at protesters who ransacked stores, threw rocks and bottles at police officers, and set cars and buildings ablaze Monday evening. The unrest began hours after the funeral of Freddie Gray, a 25-year-old black man who died in police custody two weeks ago.

“This is not protesting. This is not your First Amendment right. This is just criminal acts to a community,” Baltimore City Police Commissioner Anthony Batts said, at a press conference late Monday night. “I am extremely disappointed in what has happened in this beautiful city today.”

At least 15 police officers were injured after groups of young people began throwing objects at law enforcement officials and stomping on police cars. Batts said all officers had been released from medical care, though six continued to suffer traumatic shock. More than two dozen people have been arrested so far in connection with the violent protests.

Baltimore Mayor Stephanie Rawlings-Blake faced criticism Monday for failing to respond quickly and sufficiently to the escalating chaos. The mayor defended her decision to delay a widespread police response or call for state reinforcements, alluding to the 2014 police crackdown on protesters in Ferguson, Missouri. An overreaction could make the situation worse, she said.

“We have seen what has happened when you use too much force. We were working not to escalate,” Rawlings-Blake told reporters. "This darkest day will not define our city."

Batts said the first incidents between Baltimore police and young people began around 3 p.m. EDT, when high school students finished classes for the day. Police had information that youth were planning to gather at the Mondawmin Mall on Baltimore’s west side, and roughly 300 troops were positioned at the site when classes let out. Agitators began throwing sticks, rocks and bottles at police officers, striking several in the head and arms, before moving south and west of the mall.

Batts described how violent activity spread across the city, eventually escalating into riots. Multiple shops were looted and rampaged, including a CVS pharmacy near Pennsylvania, which rioters eventually set ablaze. Several vehicles were set on fire, and flames were ignited in the streets. Police responded by firing pepper balls and rubber bullets, injuring at least a dozen protesters, passersby and reporters.

“We planned for it. They just outnumbered us and outflanked us. We needed to have more resources there," Batts said.

A massive three-alarm fire raged through a community center building under construction on Baltimore’s east side, though fire and police officials said they are still investigating the official cause. A spokesman for the mayor and deputy fire officials told reporters they believed the fires were intentionally set. “We don’t know if it’s related to the riot,” Rawlings-Blake clarified around 11:15 p.m. EDT. “The destruction that we’ve seen is heartbreaking.”

National Guard troops arrived in Baltimore late Monday after Gov. Larry Hogan declared a state of emergency. As many as 5,000 officers from across the mid-Atlantic region could be deployed in the city by tomorrow, officials confirmed. Batts said National Guard troops would help maintain control of structures and fixed posts while Baltimore and Maryland police responded to incidents in other parts of the city.

Hogan said he would move his governor's office and cabinet from the state capital Annapolis to Baltimore on Tuesday to help oversee the police response. There appeared to be tension between Hogan and Rawlings-Blake Monday night over whether she had waited too long to call in state reinforcements.

Rawlings-Blake instituted a citywide curfew from 10 p.m. to 5 a.m., which will begin Tuesday and run through May 4, unless repealed or extended by the mayor. Police on Monday night enforced existing curfews for children 17-years-old and younger, and Baltimore city schools canceled classes for Tuesday. Batts said he hoped the curfew could help quell the violence. “I don’t know if it’s going to get worse,” he said. “I think the curfew is going to help us get the city under control.”

Family and supporters of Freddie Gray continued to speak out against the riots in Baltimore. Gray’s relatives had called for a pause in demonstrations Monday as they buried the 25-year-old man that morning. Fredericka Gray, Freddie’s twin sister, said her brother “wasn’t for this.”

“I don’t think that’s for Freddie,” she said at a press conference late Monday night. “I think the violence is wrong.”