A gas explosion and subsequent fire Wednesday night into Thursday morning at a Silver Spring, Maryland, apartment complex has killed at least two people and left dozens more injured or missing. 

The explosion occurred just before midnight at the four-story Flower Branch Apartments complex in Silver Spring, Maryland a suburb of nearby Washington D.C. Residents reported smelling natural gas just before the blast, according to local authorities. Neighbors as far as a mile away reported being able to feel the blast from their homes. According to Montgomery County police, an officer on patrol spotted the fire and part of the apartment complex collapsing while in the area and immediately called for rescue personnel. 

Maryland Fire Fire and rescue crews are seen at the site of an overnight explosion and fire that destroyed an apartment building in the Flower Branch Apartments complex on August 11, 2016 in Silver Spring, Maryland. Photo: Getty Images

Two people were killed in the incident in addition more than 30 reported injured, including some firefighters. However, because the blast and fire rendered the remaining structure of the apartment complex unstable, firefighters had to pull out before recovering all of the residents believed to be inside. The victims have not been identified.

"We still believe some people are still unaccounted for," Montgomery County Assistant Police Chief Russ Hamill said in a news conference, according to Reuters. Hamill did not specify how many people were believed to be missing. 

It took more than 160 firefighters more than two hours to put out the blaze. Meanwhile, residents were frantically trying to escape the building, with some reports of people jumping from the upper levels of the building. Local residents posted dozens of pictures and video of the fire that they had filmed on their phones on social media. 

The official cause of the fire has not been released, but some residents told NBC4 that they had smelled natural gas periodically in the days leading up to the explosion. The Montgomery County fire department responded to a call on July 25 reporting the smell of gas. Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are helping local investigators identify exactly what happened.