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• "A minimum of 20 officers have been injured during the course of the lawlessness that took place," Baltimore Police Capt. Eric Kowalczyk said. He added that some officers suffered minor injuries but did not seek medical treatment because "they wanted to stay with other law enforcement officers and continue to help protect the city."
• One person is in critical condition as a result of one of the 19 structure fires in the Maryland city, according to Kowalczyk.
• Protesters were gathered at midday Tuesday near the intersection of Pennsylvania and North avenues in Baltimore. Kowalczyk described them as peaceful, which he said is "what we're used to seeing in Baltimore." That said, about a dozen people had been arrested Tuesday, the police captain said.
Charred cars and buildings. Hospitalized police officers. Looted and damaged businesses. No school, because it might not be safe for children to go outside.
That was the stark reality Tuesday after a day and night that saw hundreds of arrests, 144 vehicle fires and 19 structure fires, according to city spokesman Kevin Harris.
"What happened ... destroyed so much of the progress that the people who actually live here have been working for," said Mayor Stephanie Rawlings-Blake, calling Monday "a very dark day for our city."
"What happened last night made sure that more people are struggling and that more people have needs, and those needs are going to go unmet because of what was destroyed."
At least 15 officers were wounded in the unrest, six of them seriously, the city's police commissioner said. As they recover, the situation on the ground remains on edge -- with yet more arrests, albeit no more violence, on Tuesday.
The tumult comes after protests across the country over the deaths of black men after encounters with police, including Michael Brown in Ferguson, Missouri; Eric Garner in New York; and Walter Scott in North Charleston, South Carolina.
This latest eruption came after days of simmering tensions over Freddie Gray, who mysteriously died on April 19, a week after Baltimore Police arrested him. Anger over his plight may have spurred Monday's violence, but Baltimore City Council Member Brandon Scott said it was also fueled by "a long, long, longstanding issue with young African-Americans."
"We're talking about years and decades of mistrust, of misfortune, of despair that it's just coming out in anger," Scott said. "No, it is not right for them to burn down their own city. But that is what's coming out of these young people."
Laquicha Harper, a 30-year-old Baltimore resident, called the violence embarrassing and heartbreaking, saying "We owe it to ourselves to do better." She was among locals who responded Tuesday morning with brooms, not rocks, to clean up the mess left behind.
"I understand that everybody is upset, I understand that tension is brewing ... I'm here, I get it," she said. "But there are better ways that we can handle our frustration. And they can't hear us when we're behaving this way."
No repeat of Monday night, governor says
If Monday was a day of destruction, Tuesday -- at least to start -- was a day to clean up, beef up security, question what just happened and try to stop it from happening again.
Maryland Gov. Larry Hogan said at noon that he didn't know of additional instances of looting, damage or violence. But he's mindful that may not be true for long, saying he's especially concerned about Tuesday night.
If there is another flare-up, Hogan said, authorities will be prepared with "as much manpower and as many resources as we can (have)."
"They are not going to be in danger, and ... their property will be protected," he said of Baltimore residents and business owners. "We're not going to have another repeat of what happened last night. It's not going to happen tonight."
Hogan declared a state of emergency Monday evening -- after a request from Baltimore's mayor around 6 p.m. -- that, among other things, expedited the deployment of hundreds of National Guard members. Up to 5,000 of them are ready to answer the call to join Baltimore police and up to 5,000 law enforcement officers were requested from around the Mid-Atlantic region, said Col. William Pallozzi of the Maryland State Police.
Rawlings-Blake has imposed a mandatory curfew from 10 p.m. to 5 a.m., which is one reason why the Baltimore Orioles postponed their Tuesday night game and the Baltimore Ravens called off an NFL draft party set for Thursday night. There was no public school Tuesday, nor were there classes at Johns Hopkins University.
"Seeing my city like this breaks my heart. But, like so many Baltimoreans, my resolve is strong," the mayor tweeted. "We will not let these deplorable and cowardly acts of violence ruin #OurCity."
Meanwhile, citizens young and old are stepping up. They include people who came out to clean up, like Harper and 15-year-old Sulaiman Abdul-Aziz, who said he saw some of the mayhem.
"I felt disappointed," Abdul-Aziz said, "because a lot of that could have been avoided if people would have started thinking before they would have done all that stuff."
'Purge' by high school students
That stuff began with word of a "purge" after school Monday starting in Baltimore's Mondawmin Mall. It echoed a movie, titled "The Purge," about a dystopian society in which, for one day each year, all laws are suspended for 12 hours.
Police Commissioner Anthony Batts said authorities knew about the "large 'purge' of high school students from across the city" and staged 250 to 300 police officers at the mall as a precaution.
But it wasn't enough, said Neill Franklin, a former Maryland State Police officer who has worked with Baltimore police. Franklin told CNN that law enforcement officers "were prepared physically, (but) they were overwhelmed by the number of students."
Police in riot gear took cover behind an armored vehicle as assailants -- the instigators appearing to be high school students, according to Batts -- hurled heavy objects at them.
"I think they thought it was cute to throw cinder blocks at police," the police commissioner said.
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."
It's not known how many, if any, of the police officers' injuries could be traced to gangs.
Senior center engulfed in flames
There were many other secondary casualties -- people who saw their neighborhoods torn apart, their homes and vehicles damaged, their hopes for stability and progress thwarted by the mayhem.
"It started off peaceful, and it ends up like this," Cindy Oxendine told CNN affiliate WBAL while sweeping rocks and glass from her street. "... I've seen stuff like this on the news in other cities, but I never thought I would see it in front of my doorstep. It's crazy."
In addition to clashes with police came dozens of fires tied to the unrest, according to a federal law enforcement source. This included one that engulfed an affordable housing center for seniors that was months away from opening.
Pastor Donte Hickman of the Southern Baptist Church, which owns the facility, said 60 units of senior housing were lost.
"My eyes have been filled with tears," he said. "Someone didn't understand that we exist in the community to help revitalize it."
Activist vows 'another night' to protest corrupt police
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."
President Barack Obama said Tuesday that "some police aren't doing the right thing" and that a lot of the tension between law enforcement and the black community stems from "a slow-rolling crisis" that has been brewing for decades. Fixing it will require more investment in cities, criminal justice reform, better funding for education and soul-searching for some police departments, he said.
Still, no angst can excuse what Obama called the behavior of "criminals and thugs who tore up" Baltimore.
"When individuals get crowbars and start prying open doors to loot, they're not protesting. They're not making a statement. They're stealing," he said. "When they burn down a building, they're committing arson. And they're destroying and undermining businesses and opportunities in their own communities. That robs jobs and opportunity from people in that area."
By Greg Botelho and Athena Jones
Athena Jones reported from Baltimore, and CNN's Greg Botelho reported and wrote this report from Atlanta. CNN's Holly Yan, Evan Perez, Jason Hanna, Dana Ford and Ben Brumfield contributed to this report.