Baltimore Riots 'Not Going to Happen Tonight,' Governor Says National guard troops were deployed in front of Baltimore City Hall today.

 -- Maryland Gov. Larry Hogan said at a news conference today the immediate need is to restore calm in Baltimore and that the city is well on its way.

"We're not going to have a repeat of last night," Hogan said. "It's not going to happen tonight."

President Obama today called the riots in Baltimore "senseless violence and destruction."

"They're not protesting, they're not making a statement. They're stealing," Obama said at an afternoon news conference in Washington. "They're destroying and undermining businesses and opportunities in their own communities.

"They need to be treated as criminals," he added.

Police in Baltimore said 235 people were arrested Monday, including 34 juveniles. Seven adults and five juveniles were arrested today.

Meanwhile, national guard troops were deployed in front of Baltimore City Hall this morning and a state of emergency was issued after violence erupted in the city Monday afternoon. The city will have 2,000 national guardsman and over 1,000 law enforcement on duty, Hogan said today.

Numerous fires were reported overnight and Baltimore police reported people throwing cinder blocks at fire engines as firefighters worked to extinguish the flames. Fifteen structure fires and 144 vehicle fires were reported, according to Howard Libit, director of strategic planning and policy at the Mayor's Office.

Baltimore City Public Schools were closed today, but will reopen Wednesday, a school spokesperson said.

Tonight's baseball game at Oriole Park between the Orioles and the Chicago White Sox has been postponed to May 28. Wednesday's game between the Orioles and the White Sox will be closed to the public.

A citywide curfew will be in effect from 10 p.m. today until 5 a.m. Wednesday. The 10 p.m. curfews will last for one week, mayor Stephanie Rawlings-Blake said, and could be extended as necessary. A 9 p.m. curfew is already in effect for children 14 and younger.

Monday’s standoff began near the Mondawmin Mall in the northwest part of the city, the Baltimore Police Department said, as the group threw bricks, rocks and other objects at officers. Protesters were seen climbing on a police cruiser and damaging several others, and fires broke out, including flames that engulfed a community center project.

At least 20 officers were injured, police said.

The unrest was sparked by the death of Freddie Gray, who died after being in police custody. Gray’s mother, speaking the night of the 25-year-old’s funeral, made a plea for peace.

“I want you all to get justice for my son, but don’t do it like this here. Don’t tear up the whole city just for him,” Gloria Darden said. “It’s wrong.”

Rawlings-Blake, speaking to reporters late Monday, decried the violence and property damage.

"People say they care about their community and want to be heard, but you can’t care about your community and do what they did," Rawlings-Blake said. "I understand anger, but what we’re seeing isn't anger, it’s destruction of a community."

Newly minted Attorney General Loretta Lynch also weighed in, condemning the “senseless acts of violence by some individuals in Baltimore.”

“The Department of Justice stands ready to provide any assistance that might be helpful,” Lynch added. “The Civil Rights Division and the FBI have an ongoing, independent criminal civil rights investigation into the tragic death of Mr. Gray.”

Get real-time updates as this story unfolds. To start, just "star" this story in ABC News' phone app. Download ABC News for iPhone here or ABC News for Android here.