BALTIMORE -- Violence swept through pockets of a low-income section of West Baltimore Monday afternoon as rioters heaved bottles and rocks at riot gear-clad police, looted a pharmacy, mall and other businesses, set police cars on fire and hurt at least 15 officers.

Images of the violence were broadcast nationwide just hours after Freddie Gray was eulogized at his funeral, and Gray's family and clergy members called for calm. Gray died of an injury he suffered while in police custody earlier this month.

The rioting did not appear to stem from protests over Gray's death. Police from surrounding communities were called in to help. Gov. Larry Hogan declared a state of emergency in the city and activated the National Guard. The troops were in Baltimore before midnight.

"I have not made this decision lightly," Hogan said. "The National Guard is the last resort in order to restore order. . . . People have a right to protest and express their frustration, but Baltimore City families deserve peace and safety."

Last night's White Sox-Orioles game was postponed out of concern that the violence would spread five miles east, toward Camden Yards.

The officers were injured -- some with broken bones and at least one rendered unconscious -- after the violence began about 3 p.m. Two officers remained hospitalized late Monday; they had been hit with items thrown mostly by school-age youths, police said. Officers in full riot gear were pelted with rocks and bottles as they moved in to arrest some of the young people who had assaulted them.

Earlier, Baltimore police said the department had received a "credible threat" that three notoriously violent gangs are now working together to "take out" law enforcement officers.

Mobs destroyed police cars, started several small fires, and invaded a check-cashing agency and sought to break into its ATM. Looters carried off armloads of merchandise from liquor stores and a CVS pharmacy at Pennsylvania and North avenues that also was set ablaze. The mobs for a time seemed undaunted by police and even cut holes in a fire hose as firefighters tried to douse the blaze at the pharmacy.

By nightfall, 27 people had been arrested.

Late Monday, Mayor Stephanie Rawlings-Blake blamed the violence on "thugs who always want to incite violence and destroy our city." She added, "Too many people have spent generations building up this city for it to be destroyed by thugs who, in a very senseless way, are trying to tear down what so many have fought for. Tearing down businesses, tearing down and destroying property -- things that we know will impact our community for years."

In response to the violence, she said, the National Guard would help city police, and she set a citywide daily curfew for at least a week starting Tuesday, from 10 p.m. to 5 a.m. for adults and from 9 p.m. to 5 a.m. for children aged 14 and younger. Baltimore public schools announced that they would be closed today.

Yesterday's violence, along with a protest march on Saturday night that ended with mayhem, marred what had been a week of peaceful protest after Gray's death. Gray, 25, died of a severe injury to his spine a week after police subdued him in an April 12 arrest. Federal and local authorities are trying to determine how the injury occurred. The Justice Department has opened a preliminary civil- rights inquiry into Gray's death.

Gray's name was added to the roster of black men who have died in recent months in encounters with police, including Michael Brown in Ferguson, Missouri, Eric Garner in Staten Island, and Walter Scott in North Charleston, South Carolina.

Police have declined to specify the races of the six officers involved in his arrest, all of whom are suspended with pay amid the investigation into the death.

"Every time you come into this community you bust heads," Ochilo Kelo, 35, said to police officers as they moved into the area of the CVS, near where Kelo lives. "If we could just talk, all this would stop. This is my city. I don't want this. . . . Eight hours of peaceful protest and all we got to show for it is a riot."

Officers formed a number of human cordons to prevent the violence from moving to the downtown area that includes hotels, restaurants and Camden Yards.

The Rev. Duane Simmons, pastor of Simmons Memorial Baptist Church, stood in front of his church a block from the burned-out CVS. "It is heart-wrenching, but it is something that we have been anticipating," he said. "People are frustrated. These folks have had enough." He left his church to attend a meeting of church leaders who sought to come up with a solution to the violence.

Late yesterday, Gray's twin sister, Fredericka Gray, condemned the rioting. "I don't agree with the violence that they're doing to the city -- it's too much," she told reporters. "I don't think that's for Freddie. I think they're doing violence for something else." Gray's family had hoped to organize a peace march later in the week, said William Murphy Jr., an attorney for the family.

Police declined to link protests over Gray's death to the criminal activity Monday, when TV cameras captured looters casually walking out of the CVS, liquor stores and a check-cashing store. Some rioters posed for selfies in front of a destroyed police car.

The possibility of Monday's violence began to emerge about 10 a.m., when social media users warned of large crowds, looting and rioting at Mondawmin Mall some time after 2:30 p.m. or after school. Many businesses nearby and others downtown closed early in anticipation of trouble. Officials "pre-deployed" near the mall in response to the social media information, said police Col. Darryl DeSousa. Police found about 75 to 100 school-age youths in the area, and a confrontation quickly escalated, he said.

President Barack Obama spoke with Hogan and Rawlings-Blake Monday and was said to be receiving updates from U.S. Attorney General Loretta Lynch.

"I'm at a loss for words," Rawlings-Blake said. "It is idiotic to think that by destroying your city that you're going to make life better for anybody."

With AP and Bloomberg News

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