Firefighters spent Christmas morning battling a five-alarm fire in Boston's historic North End neighborhood.

No residents were hurt, but two firefighters sustained minor injuries, according to a Boston Fire Department spokesperson.

The department says they responded at 4:15 a.m. Sunday to a four-unit brick apartment building at 52 Hull St. The building is home to six residents, but BFD says no one was inside at the time of the fire.

The roof of the building at the intersection of Hull and Snow Hill Streets has collapsed. The department estimates about $4 million in damages.

Investigators continue to search for the cause of the fire.