An explosion and fire that collapsed part of a Silver Spring apartment building Thursday morning left three people seriously injured. Several residents were unaccounted for, fire officials said.

Crews found heavy fire on multiple floors of the four-story, garden-style apartment building around 10:30 a.m., according to Montgomery County Fire and Rescue Service spokesman Pete Piringer. 

A significant portion of the Friendly Garden Apartments had collapsed before crews arrived.

Firefighters rescued several residents and, according to WUSA9, witnesses said several residents jumped from the burning building.

Fire Chief Scott Goldstein told WUSA9 that 10 people were injured, with three listed in critical condition. 

"It is too early for me to say what initiated this," the chief said. "We are working through a wide range of concerns and possibilities are focus is on life safety at this time," said the chief said.

Heavy equipment was called in to the scene to help remove towering walls adjacent to the debris due to threats of additional collapse. Once stabilized, Goldstein said firefighters will search the rubble of the building. 

A K9 was brought in to search for the unaccounted residents and crews were checking from the perimeter.

Piringer said over 150 firefighters were summoned to the scene to fight the fire, and treated the injured.

Several residents refused transportation to the hospital.

Officials said that three adjacent buildings were not safe for residents to occupy.