A citywide curfew is underway in Baltimore, one day after a violent riot by hundreds of people, including teens. Still, hundreds of people are on the streets, and some have gotten aggressive against officers.

Fifteen minutes after the start of the city-wide curfew, hundreds of people are still on the streets of Baltimore. Police in riot gear have started to move toward the crowd. Volunteers are still urging the crowd to go home. Police have told media they can stay but residents are being told to leave.

Smoke bombs or fireworks thrown from the crowd sent acrid smoke billowing around a square where dozens of riot police stood with shields in front of them, lined shoulder to shoulder against the crowd. Police advanced some steps forward into the intersection but there were no immediate signs of any arrests being made.

According to local reports people scattered, running in different directions down side streets. The smoke from the incendiary devices wafted through the square. Local reporters said the tension rose after people threw water bolts and other debris. People covered their faces as they ran, some coughing.

Baltimore Police tweeted at 10:32 p.m. that "Officers are now deploying pepper balls at the aggressive crowd."

Capt. Eric Kowalczyk said at least 20 officers were hurt Monday during the chaos that started as a "high school event" and escalated. He said nearly three dozen juveniles were arrested and more than 200 adults were taken into custody after people set fire to cars and businesses and looted stores. Nearly 150 cars were burned.

 Baltimore police spokesman Capt. Eric Kowalczyk said police were using a variety of measures to inform the public about the curfew.

Shortly before the curfew was to go into effect he said that police in cruisers were driving through neighborhoods using their cars' public address systems to notify residents of the 10 p.m. curfew. He said police were also broadcasting the message using a police helicopter. Kowalczyk said the city was also using its Reverse 911 system to notify residents of the curfew.

Maryland's governor said there will be 2,000 National Guard troops and more than 1,000 police officers on the streets to enforce the 10 p.m.-5 a.m. curfew after riots in the wake of Freddie Gray's death. He died after injuries in police custody.

Baltimore Public Schools CEO Gregory Thornton said in a notice posted on the school system's website that schools will be open on Wednesday. The notice also said that after-school sports and clubs will also take place.

Baltimore Mayor Stephanie Rawlings-Blake said schools had no choice but to close Tuesday since many teachers called and said they wouldn't work the day after the riots.

National Guardsmen took up positions across the city and hundreds of volunteers began sweeping the streets of broken glass and other debris Tuesday.

"We're not going to leave the city unprotected," Maryland Gov. Larry Hogan vowed during a visit to a West Baltimore intersection where cars were burned and windows smashed the night before.

State Police and law officers from other jurisdictions joined Baltimore police in patrolling the streets. National Guardsmen in riot helmets with face shields surrounded City Hall, standing behind bicycle-rack barriers.

It was the first time the National Guard was called out to quell unrest in Baltimore since 1968, when some of the same neighborhoods burned after the assassination of the Rev. Martin Luther King Jr.

As firefighters doused smoldering fires around the city, many lamented the damage done by the rioters to their own neighborhoods.

Hundreds of volunteers helped shopkeepers clean up as helmeted officers blocked a stretch of North Avenue in the neighborhood where Freddie Gray, 25, was arrested earlier in this month in a case that has become the latest flashpoint in the national debate over the police use of deadly force against black men.

Hardware stores donated trash bags and brooms, and city workers brought in trucks to haul away mounds of trash and broken glass.

With schools closed, Blanca Tapahuasco brought her three sons, ages 2 to 8, from another part of the city to help sweep the brick-and-pavement courtyard outside a looted CVS pharmacy.

"We're helping the neighborhood build back up," she said. "This is an encouragement to them to know the rest of the city is not just looking on and wondering what to do."

CVS store manager Haywood McMorris said the destruction didn't make sense: "We work here, man. This is where we stand, and this is where people actually make a living."

The rioting started in West Baltimore on Monday afternoon - within a mile of where Gray was arrested - and by midnight had spread to East Baltimore and neighborhoods close to downtown and near the baseball stadium.

The rioters set police cars and buildings on fire, looted a mall and liquor stores and hurled rocks, bottles and cinderblocks at police in riot gear. Police responded occasionally with pepper spray or cleared the streets by moving in tight formation, shoulder to shoulder.

At least 20 officers were hurt, including six who were hospitalized, police said. There were 144 vehicle fires, 15 structure fires and nearly 200 arrests, the mayor's office said.

"They just outnumbered us and outflanked us," Baltimore Police Commissioner Anthony Batts said. "We needed to have more resources out there."

The rioting was the worst such violence in the U.S. since the turbulent protests that broke out over the death of Michael Brown, the unarmed black 18-year-old who was shot by a white police officer in Ferguson, Missouri, last summer.

"I understand anger, but what we're seeing isn't anger," Baltimore Mayor Stephanie Rawlings-Blake lamented. "It's disruption of a community. The same community they say they care about, they're destroying. You can't have it both ways."

State and local authorities found themselves responding to questions about whether their initial response had been adequate.

Rawlings-Blake waited hours to ask the governor to declare a state of emergency, and the governor hinted she should have come to him earlier.

"We were all in the command center in the second floor of the state House in constant communication, and we were trying to get in touch with the mayor for quite some time," Hogan said at a Monday evening news conference. "She finally made that call, and we immediately took action."

Asked if the mayor should have called for help sooner, however, Hogan replied that he didn't want to question what Baltimore officials were doing: "They're all under tremendous stress. We're all on one team."

Rawlings-Blake said officials initially thought they had gotten the unrest under control.

Maryland National Guard spokesman Lt. Charles Kohler said that about 2,000 members would be deployed through the day and that the force could build to 5,000.

"We are going to be out in massive force, and that just means basically that we are going to be patrolling the streets and out to ensure that we are protecting property," said Maj. Gen. Linda Singh, adjutant general of the Maryland National Guard.

Also, State Police said they were putting out a call for up to 500 additional law enforcement officers from Maryland and as many as 5,000 from around the mid-Atlantic region.

Attorney General Loretta Lynch, in her first day on the job Monday, said she will send Justice Department officials to the city in the coming days. And the governor said he is temporarily moving his office from Annapolis to Baltimore.

Gray was arrested April 12 after running away at the sight of police, authorities said. He was held down, handcuffed and loaded into a police van. Leg cuffs were put on him when he became irate inside. He died of a spinal cord injury a week later.

Authorities said they are still investigating how and when he suffered the injury - during the arrest or while he was in the van, where authorities say he was riding without being belted in, a violation of department policy. Six officers have been suspended with pay while the investigation continues.

While they are angry about what happened to Gray, his family said riots are not the answer.

"I think the violence is wrong," Gray's twin sister, Fredericka Gray, said late Monday. "I don't like it at all."

In 1968, when Baltimore and many other U.S. cities erupted in flames over the assassination of King, the state of Maryland called up 6,000 Guardsmen to restore order in the city, and 2,000 active-duty federal troops were sent in, too.

Standing in front of the burned-out CVS drugstore Tuesday, the mayor lamented that the neighborhood was still recovering from the riots of the 1960s.

"We worked so hard to get a company like CVS to invest in this neighborhood," she said. "This is the only place that so many people have to pick up their prescriptions."