This post has been updated.

Seventeen people were rescued and dozens more were evacuated after heavy fire ripped through a Montgomery County apartment building Friday morning, officials said.

According to Assistant Fire Chief Scott Graham, the three-alarm fire began shortly before 7:30 a.m. at the Woodlake Apartments in the 14000 block of Castle Boulevard in Burtonsville. Authorities believe the fire was caused accidentally by a malfunctioning electrical switch in the first floor unit of the building.

The blaze ignited in the rear of one of the townhomes and quickly spread to the upper floors and the roof of the building, he said.

More than 100 firefighters from Montgomery County and neighboring jurisdictions worked to extinguish the fire, officials said.

More than 70 other people have been displaced from their units. The fire department estimates about $1.5 million worth of damage.

Only minor injuries have been reported, according to officials.

The apartment building’s management is working with the American Red Cross to assist the displaced residents, officials said.