The blast lifted the roof of the building up and sent its facade flying across the street, as seen on nearby security camera footage passed to local media.
The explosion then ignited a fire that was visible for a long distance. Observers, including a local news crew, reported the blaze was so intense that its heat could be felt a significant distance from the flames.
Montgomery County Fire & Rescue Chief Scott Goldstein told reporters on Thursday afternoon that 10 people had been taken to area hospitals, three of whom had suffered serious injuries.
“There are unaccounted-for people,” he added, but couldn’t say how many or why, stressing that some people may simply be at work.
In addition, the blast has damaged three other buildings, which have now been declared unsafe, displacing dozens of people and families.
Goldstein said “it’s too early to speculate” on the cause of the explosion.
However, one resident told NBC Washington there was a “heavy smell of gas” in the building in the hours before.
Another massive explosion in nearby Silver Spring leveled an entire apartment complex in 2016, killing seven people. According to an investigation by the National Transportation Safety Board, that explosion was caused by a faulty vent and regulator on a gas line.
As Sputnik has reported, the United States’ gas infrastructure is aging and brittle, with the Department of Transportation’s Pipeline and Hazardous Materials Safety Administration (PHMSA) burdened by a shortage of regulators to monitor safety and a set of regulations written under the watchful eye of the industrial giants they are expected to oversee.
"This isn't like the fox guarding the hen house," Carl Weimer, executive director of the Pipeline Safety Trust, a public charity that promotes fuel transportation safety, told Propublica in 2012. "It's like the fox designing the hen house."