The Bureau of Alcohol, Tobacco, Firearms and Explosives is assisting county fire investigators searching for the cause of Wednesday's massive Maryland apartment building blaze that killed two, officials said.

The inferno, which was reportedly proceeded by a loud explosion, injured three firefighters and 31 other people, authorities said during a Thursday afternoon news conference.

At least five people were still unaccounted for.

Police said they were aware of reports that area residents detected the odor of gas before the fire and revealed that a 911 call from the neighborhood was placed on July 25 reporting the smell of gasoline. Firefighters responded to that call and officials said they believed the report had been "cleared."

The Montgomery County Fire and Rescue Service said first responders were dispatched to the scene in Silver Spring just before midnight Wednesday and that the fire was under control by Thursday morning.

Fox 5 DC reported that an explosion sparked the roaring inferno and that nearby buildings suffered collateral damage.

"When we arrived on the scene, we found people doing rescues using ladders from construction and paint trucks," Montgomery County Fire and Rescue Service Chief Scott Goldstein said at a news conference.

"People were dropping children and jumping out of other windows. Everybody was getting out of the building as rapidly as possible."

Capt. Oscar Garcia told the Associated Press that the three firefighters hurt battling the blaze suffered non-life threatening injuries. The extent of the others’ injuries was unknown.

Garcia said the fire involved two or three buildings.

About 100 people were displaced and a shelter was opened at a community center nearby. Residents of nearby buildings that were not affected by the fire were allowed to return to their homes after several hours.

Hours after the fire was put out, smoke still was rising from the four-level garden style apartment building. Debris from the blast scattered nearly 200 feet, including what appeared to be an apartment door blown all the way across a two-lane road and parking lot. Brightly colored bras hung from a tree in front of the apartments, apparently from a dresser drawer launched in the explosion. Windows across the street were broken.

The Associated Press contributed to this report.