The blast — near Labyrinth and Reisterstown Roads — happened a little before 10 a.m. and killed at least one woman, according to the Baltimore City Fire Department.
"We're prepared to be here throughout the night, as long as it takes," city fire spokeswoman Blair Adams told reporters late Monday afternoon.
"We're working diligently on trying to make sure that we comb through every area to determine if there are any (more) victims inside (under rubble)."
The cause of the gas line blast was not immediately known.
"It’s a labor-intensive rescue," Adams said Monday morning. "Again, it was a major gas explosion so you had homes that were pretty much crumbled — a ton of debris on the ground that we're trying to comb through."
The blast happened a short walk away from Reisterstown Road Plaza, a major retail hub in the region.
It wasn't immediately clear how many people would be left homeless by the blast. First responders want to find them so the Red Cross can provide hotel rooms, Mayor Jack Young said.
"A lot of houses have been destroyed, a lot of windows have been shattered," Young said. "We just want to make sure we take care of these people."
Neighborhood resident Vircha Dehoney said she was in her basement about to go on to a Zoom call for work when the blast happened.
"All of a sudden, there was this loud boom, like it shook me," Dehoney told NBC affiliate WBAL. "I've never heard anything like it in my life. I didn't know what it was."
She emerged from the basement, opened the door, and saw a blank space where three row homes — synonymous with the residential neighborhoods of Baltimore — used to be.
"I was hysterical. I went to pieces," Dehoney said. "I've never heard anything like that in my life. Never. ... I'm grateful to God for being here."
She said if she wasn't a neighborhood resident, she would have simply believed no houses had ever existed where the explosion happened.
"It looked like there were no houses there for a long time," Dehoney explained. "Like there had never been houses there. I know they were there, they were there last night."
Baltimore Gas and Electric Company said it was trying to restore electricity to customers who lost power, but warned residents across northwest Baltimore they could be without gas for most of Monday as the search and rescue continues.
“BGE is continuing to work to turn the gas off to this area. We’re now working to turn off the gas main, which will likely take customers out who’ve been largely unaffected by this event," BGE spokeswoman Linda Foy told reporters late Monday afternoon.
"But that’s what we need to do in order to make the area safe.”
Firefighters were in full gear as they battled the debris and 90-degree heat with high midday humidity that made it feel like 100 degrees.
"It's a lot of work by hand, a lot of back-breaking work," International Association of Fire Fighters Local 734 President Rich Langford told NBC News. "It's extremely hot and our guys are pushing through to get the job done."