A pallor reminiscent of an earlier desperate era hung over this city Tuesday as National Guardsmen with rifles and police in riot gear looked on while fire-scarred buildings smoldered, burnt cars were towed away and the rocks hurled by rioters were swept from the streets.

The acrid smell of smoke lingered, just as it had in Harlem, Watts, Newark, Philadelphia, Chicago and Washington during the tumultuous decade of the 1960s.

Soldiers dressed as if for combat and police in full riot gear patrolled the streets. Sand-colored military Humvees mixed in with police squad cars rolling through neighborhoods. Merchants and neighbors came out to clean up shattered stores and streets strewn with debris.

There was no repeat of Monday’s violence, in which dozens of people — many of high school age — pelted police with rocks and bottles, looted several stores and set things ablaze.

But at 10 p.m., when a newly imposed curfew went into effect, tensions between police and several dozen peaceful protesters became heated. A loudspeaker from a hovering helicopter reminded the crowd of the curfew and asked people to go home.

As a 10 p.m. enforced curfew loomed, the mood on the streets in Baltimore shifted from positivity to a tense stand-off with law enforcement that was quickly dispersed. (Whitney Leaming/The Washington Post)

The request was met with expletives, and rocks were thrown at a line of police in riot gear. Police unleashed smoke cannisters and shot pepper balls. The line moved forward slowly, while officers banged their shields. Some in the crowd, including a few who had donned bandannas as masks, tossed plastic or glass bottles and shouted profanity.

But most of the crowd dispersed with the show of force, and the mood began to ease. Seven people were arrested for curfew violations and three others arrested on other charges, police said.

For most of Monday, though, the city was generally subdued and even turned hopeful as a band played in the street and people sang and prayed.

Talk of the rioting supplanted conversation about the controversial death of Freddie Gray after he was taken into police custody April 12, which had been the primary topic of discourse before Monday’s mayhem. The outburst of lawlessness that erupted after his funeral Monday seemed inextricably linked to his death, but city leaders and Gray’s family said it was born out of a more general frustration that found voice in his death.

“It breaks my heart,” Mayor Stephanie Rawlings-Blake (D) said, with tears welling in her eyes, at an appearance with leaders at Bethel A.M.E. Church in West Baltimore. “We will recover. We will be better on the other side of things.”

She said she regretted calling the rioters “thugs” at a Monday night news conference.

Events leading to Gray’s arrest and hospitalization

“We don’t have thugs in Baltimore,” she said. Then, referring to a recent skit by President Obama at the White House Correspondents’ Association dinner, she added: “Sometimes my own little anger translator gets the best of me. They’re going to regret what they’ve done, but it’s too late.”

Maryland Gov. Larry Hogan (R) was less charitable about the rioters Tuesday, calling them “roving gangs of thugs.”

“Criminal activity will not be tolerated,” Hogan said after meeting with community leaders. “We are not going to have another night of what happened last night.”

From the White House, Obama made an impassioned call for Americans to do “some soul searching” in the wake of the rioting, arguing that the United States has faced “a slow-rolling crisis” over race and economic opportunity in urban areas.

The president said the violence in Baltimore took away from peaceful protesters who have expressed “real concern and outrage over the possibility that our laws were not applied evenly in the case of Mr. Gray.”

“When individuals get crowbars and start prying open doors to loot, they’re not protesting, they’re not making a statement — they’re stealing,” the president 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 rob jobs and opportunity from people in that area.”

Authorities said about 250 people were arrested during the unrest that began Monday afternoon, and 20 police officers have been injured. They said blanket coverage of what took place provided ample video to identify criminal acts.

The global reach of that vivid coverage was made evident when members of the Islamic State took to Twitter to claim the rioters as fellow “rebels.” One tweet said, “rebels destroy cars of oppressive militarized police in Baltimore.”

With a 10 p.m. citywide curfew in place until next week, the Baltimore Orioles canceled Tuesday night’s 7:05 p.m. game. They said Wednesday’s game will go on, but it will be closed to the public. The team also changed an evening game scheduled for Thursday to an afternoon start and said a three game homestand against Tampa Bay would be played in St. Petersburg, Fla., instead.

Many offices, including federal buildings, were closed Tuesday or sent workers home early. The courts, the science center, the National Aquarium and two commercial malls were shuttered.

Public schools remained closed Tuesday, and there were concerns that some children would go hungry because of it. Eighty-four percent of the city’s school children qualify for free or reduced-price lunches. Schools were scheduled to open as usual Wednesday.

Baltimore Police Commissioner Anthony W. Batts also responded to mounting criticism from those who said officers should have been more aggressive when Monday’s rioting began with swarms of young people who had just gotten out of school.

“Because they’re 14-, 15- , and 16-year-old kids out there. Do you want people using force on 14- , 15- 16-year-old kids?” Batts said.

The most threatening moment of the afternoon came at the intersection where the CVS pharmacy burned Monday. When several people threw a few items toward a line of police in riot gear, other people linked arms and some raised their hands to quell the outburst.

An unidentified man with a microphone pleaded with those throwing to stop.

“This emotional stuff is not going to work,” he said.

The Rev. Al Sharpton urged people gathered outside City Hall to refrain from violence. “Every brick thrown is a potential roadblock to justice for Freddie Gray,” he said. “We’re fighting violence, not adding to it.”

State officials said they planned to have 2,000 National Guard troops in the city by nightfall Tuesday, augmented by 400 state troopers and police from surrounding communities, Pennsylvania, New Jersey and the District.

Even with the heavy police presence, much of the city seemed in a mood to cleanse itself from the images and debris of Monday night’s violence.

“We saw people coming together to claim our city, to clean our city and to help to heal our city,” Rawlings-Blake said.

Hundreds of people wielding brooms, dustpans, trash cans and even small bulldozers took to the blocks around the epicenter of the rioting in an impromptu cleanup effort. Some handed out water and trash bags, while others plucked trash from vacant lots and picked up broken glass.

Antoinette Rucker, 27, was typical. The woman from Baltimore County loaded a large, black trash can in her car and headed down to the city to clean up.

“I didn’t have to work, so I wanted to do my part,” Rucker said.

Activists shouted through bullhorns, a man registered people to vote, a woman burned incense and a group broke out in song with “Amazing Grace.”

Monica Mitchell said she felt compelled to do something. “My mother always taught me to control the controllable,” she said.

With gloves and garbage bags, she arrived at Pennsylvania and West North avenues, where much of Monday’s violence was centered, just after 5 a.m. A rake in her hand, she smiled as an orange sunrise cascaded over the city.

Randy Howell, 55, nailed boards over the windows of the stone rowhouse near the corner of North Mount and Baker streets that has been in his family since the 1950s. He thinks looters torched the convenience store next door and that the flames spread to his roof.

Howell estimated the damage to his house at $50,000. He said it would take a lot of work to keep it from becoming one more boarded-up home in West Baltimore.

“We are going to make it into a project — a lot of tender love and volunteers,” Howell said.

During the afternoon, a group of six musicians calling themselves the Baltimore Brass Factory played jazz near the burned CVS, breaking up the constant hum of crowd chatter with familiar tunes. “It’s the healing of music,” said band member Clarence Ward III, who played the trumpet. “That’s how I can best help people get their mind off the negativity. It’s all about putting some love in the air.”

By evening, hundreds of people walked near the looted CVS chanting: “We love Baltimore. We want peace.” They marched through the street, children holding hands with mothers. “Nice and peaceful,” one mother said to her son.