Firefighters rescued people trapped inside a burning apartment building in Gaithersburg early Saturday morning.

The fire forced dozens of people out of their home on one of the coldest days of the year.

It started at about 4:45 a.m. in the 800 block of Quince Orchard Boulevard at the Potomac Oak Condos.

Firefighters reported seeing heavy smoke and flames when they arrived.

Crews had to rescue people who were trapped inside. No residents were hurt, but a firefighter was taken to a hospital for smoke inhalation.

More than 100 firefighters responded to the scene.

Officials described the damage as significant. Investigators are working to figure out what sparked the fire.