A three-alarm blaze in the Inner Sunset on Saturday night killed one resident, displaced multiple families, and injured a firefighter.

Just before 9:45 p.m., a fire erupted at 1806-1810 Eighth Ave. near Ortega Street. According to SFGate, more than 100 personnel responded to the scene, and the fire was contained just after midnight. The blaze was so intense, smoke and haze were detected as far away as the Lower Haight.

Because the three-level building is below grade, firefighters could only access the first story from the street. The rear of the structure is feet away from a steep incline, which helped to create a chimney effect that made the blaze more intense and difficult to extinguish, CBS5 reported.

"When we show up on the street address in front and the building is built down in the hill in the back we have to go down towards the fire and fight that heat. It's very dangerous and a harrowing situation," said San Francisco Fire Department Asst. Chief Kevin Burke told ABC7.

Longtime resident Jessica Castro, who reportedly lived in the rear unit, is the sole fatality. The American Red Cross is assisting 12 people who have been displaced, and the cause of the fire is still under investigation.