• There were nearly 200 arrests, 144 vehicle fires and 15 structure fires in Baltimore during the unrest that began Monday, said Howard Libit, the city's director of strategic planning and policy.

• More than 500 National Guard members are in Baltimore on Tuesday morning with "hundreds more on the way," the Maryland National Guard reports.

On top of that, Baltimore police warned of a "credible threat" that gangs including the Black Guerilla Family, Bloods, and Crips had agreed to team up to "'take out' law enforcement officers."

BALTIMORE—National Guard troops fanned out through Baltimore, shield-bearing police officers blocked the streets and firefighters doused still-simmering blazes early Tuesday after riots, looting and violent unrest engulfed swaths of the city Monday.

The unrest came just hours after thousands of people attended a funeral for Freddie Gray , a 25-year-old black man who died in police custody earlier this month.

BALTIMORE—Riots, looting and violent unrest engulfed swaths of this city Monday, thrusting it into upheaval just hours after thousands of people attended a funeral for Freddie Gray , a 25-year-old black man who died in police custody earlier this month.

Fifteen officers were injured, and at least 27 people were arrested as Baltimore became the latest national flash point for race relations and law enforcement.

“We’re seeing unprecedented violence throughout the city,” Darryl DeSousa, chief of patrol for the city police department, said at an evening news conference.

Maryland Gov. Larry Hogan declared a state of emergency Monday evening, activating the Maryland National Guard, which planned to support local police ranks. Maryland State Police troopers arrived on the scene earlier, and thousands of officers from regional forces prepared to head into the city to provide backup.

Mayor Stephanie Rawlings-Blake imposed a citywide 10 p.m. to 5 a.m. curfew beginning Tuesday and lasting at least a week.

Deray McKeeson, a community organizer who was active in Ferguson and is now in Baltimore, said that while he doesn't condone using destruction and violence, he understands it as a way some vent frustrations. "Broken windows are not broken spines," he said.

McKeeson said the Baltimore vandalism, even the injuries to some officers, doesn't compare to the lost lives of Gray and other blacks at the hands of police. That's why he said protesters will remain out in full force, rallying against what they see as systemic injustice.

"Police have continued to kill people," the activist said. "Tonight will be another night where people come out into the streets to confront a system that is corrupt."