The Burlington Fire Marshal’s Office is trying to determine the cause of a three-alarm fire in the Old North End.

According to the Burlington Fire Department, it started just after 9:30 p.m. Friday at 47 Cedar Street. The structure is a two-story, two-unit apartment building. One person was inside, but they got out safely on their own and no firefighters were hurt.

Crews say the basement and the first-floor unit sustained heavy damage from the flames. Firefighters prevented the flames from reaching the second floor or the attic, but the second-floor unit took moderate smoke damage. They say an accumulation of personal belongings on the first floor made the building difficult to enter.