The fire happened in a six-story building on Eddy Street in San Francisco's Tenderloin neighborhood. Crews worked throughout the day to repair the smoke and water damage.
The fire started on the second floor of the six-floor building. Firefighters say it started in the light well where someone had discarded a cigarette.
The fire burned up the air shaft to the fourth floor where firefighters were able to advance on it and bring it to a stop. Flames flared up again at some point, and the fire make its way to the sixth floor of the building.
Crews had to help at least one resident out of the building. The resident was taken to a nearby hospital for treatment from smoke inhalation.
Most of the 40 units in the building were not damaged by the fire, but none of the residents have been allowed to return because of the repair work that needs to be done.
"I looked around, looked through the bathroom window, and I saw the fire just pouring down from the inside window," said resident Sean Means. "There's an inside light well and there was fire dripping down into the light well."
Joanna England had just enough time to gather some belongings and leave.
"Grabbed the cat, put on whatever things I could find and just got out," England said.
The apartment building was nearly 100 percent occupied at the time of the fire. Volunteers with the American Red Cross have helped at least 20 people find temporary shelter.
Many residents were directed to the City of Refuge Church in the South of Market area.