About 75 firefighters battled a blaze early Friday at an apartment building in upper Montgomery County.

Officials said the fire broke out around 5:30 a.m. on the third floor at the Cider Mill apartments in the 18000 block of Lost Knife Circle in the Gaithersburg area.

At least a dozen people were evaluated for possible medical treatment, and six patients — four adults and two children — were transported to a hospital. One of the adults was hurt after possibly jumping from the low-story building, officials said. That person is said to have a “traumatic injury,” according to fire officials.

About a dozen people were displaced after the blaze.

Officials said the main fire damage was in the living room and kitchen. The cause of the fire is under investigation.