Silver Spring, MD – A massive explosion and fire leveled a Silver Spring-area apartment building Thursday morning, sending 10 people to the hospital and leaving others missing as authorities searched the smoldering rubble.

Three people were rushed to the hospital in critical condition, while seven others suffered less serious injuries, Montgomery County Fire Chief Scott Goldstein said at a Thursday afternoon news conference.

Goldstein said several people remained unaccounted for and that K-9s had alerted people might trapped below the collapsed jumble of brick, steel, glass and concrete at the Friendly Garden Apartments.

About 100 people were displaced by the explosion, including 35 in the building that was destroyed in the 2400 block of Lyttonsville Road, Goldstein said. Two other apartment buildings were damaged in the six-building complex and are not safe to inhabit for the time being.

Sylvia Bunyasi, 48, was at home in a nearby building.

“The flames looked like they were going to reach the trees,” Bunyasi said. “The building was totally engulfed. We could feel it; we could feel how hot it was.”

The cause of the blast was under investigation Thursday, but Goldstein said there had been no reports of gas leaks at the complex since Jan. 1. Some residents reported smelling gas before the blast.

“It is too early for me to say what initiated this,” Goldstein said. “We are working through a wide range of concerns and possibilities.”

Some firefighters and rescue dogs were able to carefully walk atop the rubble pile on Thursday. The dogs are trained to detect bodies that are both alive and dead. The dogs indicated possible “alerts” that at least one body was under the rubble, Goldstein said.

Goldstein said the risk was very high for firefighters, with two unstable, unsupported walls — at least 30 feet high — looming over the rubble. Equipment was being brought in to knock down the walls.

“We will continue to work diligently until all are accounted for,” Goldstein said.

The explosion and fire occurred around 10:30 a.m. Goldstein said crews arrived to find all four stories of the building engulfed in flames. Fire department spokesman Pete Piringer said the scene was harrowing: “We have catastrophic damage.”

He went to the rear of his townhouse, and looked out a window to a destroyed apartment building about 200 feet away. Five seconds later, he said, he started to see flames. Thirty seconds after that, he said, he saw the front wall of the building fall forward.

“People were running out of the place,” Gautam said.

He saw a woman hanging out of a second-story window, holding a very young child. A man below found something to climb on, reached out, and was able to grab the child’s feet to rescue the child, Gautam said.

“She handed him the kid,” Gautam said.

Tito Garcia, 40, was showering Thursday morning when he felt his apartment shake in a building near the blast.

Garcia grabbed his 13-year-old son and ran out of his unit with Bunyasi. They tried exiting from the back of their building, but the pathway was blocked off with debris engulfed in flames.

Entire sections of the building opposite theirs — 2405 — had fallen off, Garcia said.

Steve Inman, who lives nearby, rushed to the scene of the blast after hearing a “big boom.” He said the front of the building had fallen away and the top had been sheared off. He said he helped evacuate people from a portion of the building that had not collapsed.

“I was able to get a mother and an infant out first — that was when the fire really started getting up,” Inman said. “I busted on a few doors to get some extra people out.”

Crews from Pepco and Washington Gas were on the scene examining the structures and power and gas lines. Goldstein said the recovery would be a multiday operation. Crews planned to work until dark Thursday night and resume operations Friday morning.

By noon Thursday, dozens of residents from Friendly Garden and surrounding apartment complexes had gathered along Lyttonsville Road.

The smell of smoke and gas hung in the air as first responders brought people out in stretchers and placed them in ambulances.

Pablo Deleon, 21, said he was sleeping in his apartment in a nearby complex, Paddington Square, when he heard a massive boom.

When he exited his room, all he could see was smoke, he said.

“It was just mass hysteria, giant, giant flames,” he said.

Jibreel Seid, 68, heard about the explosion from his wife. Seid, who is originally from Ethiopia, said his family was one of many immigrant families who lived in Friendly Garden. He had been at work when his wife called saying that the building next to theirs had caught fire.He rushed home to try to get his family’s immigration documents from his first-floor unit but firefighters would not let him through. There was a chance that the fire could spread, they told him.

The explosion was reminiscent of another nearby. In August 2016, a natural gas blast killed seven people and injured dozens more at the Flower Branch Apartments in Silver Spring. That blast also left a gutted shell where a building once had been.

Montgomery County Executive Marc Elrich (D) was at the building Thursday and promised a thorough investigation, and government assistance to all who needed it. He said the building that was destroyed contained affordable housing units. He called the scene “flat-out depressing.”

“It was kind of horrifying when you look at a building and see it gutted and walls down,” Elrich said. “You see all the debris piled up and all you can think is, ‘What happened to the people?’ ”

Rock Creek Forest and North Chevy Chase elementary schools canceled outdoor activities for the day, such as recess, said Montgomery County Public Schools spokesman Christopher Cram. Cram said students affected by the explosion and their families are being connected with county support.

The nonprofit group that manages Friendly Garden did not respond to a request for comment Thursday.

Maryland Gov. Larry Hogan (R) tweeted shortly before noon that his office has been in contact with county officials and with emergency officials in state government.

“Please keep all those involved, including our first responders, in your prayers,” Hogan wrote.

Authorities are scheduled to provide updates on the blast at 9 a.m. Friday.