Seventeen people were displaced and a firefighter was hurt after leaping from a fourth-story window during the battle to contain a three-alarm fire Monday in San Francisco's Hayes Valley district.

The fire in the four-story, eight-unit apartment building at 52 Page Street, between Market and Gough streets, was reported at 5:08 p.m.

Burning on both the third and fourth floors, flames eventually caused sections of the roof to cave in, and the rear stairs caught fire, making access more difficult

San Francisco fire Lt. Ken Smith said advancing smoke inside the residential four-story building on 52 Page Street forced a firefighter out of a window and onto the roof of an adjoining building 12 feet below. The firefighter sustained ankle and knee injuries in the fall but was able to rejoin his unit, Smith said.

All residents were accounted for and unharmed, though someone's cat was still missing, Smith said.

The lieutenant called the blaze "stubborn" and said 125 firefighters were summoned to extinguish it during the three-alarm response.

First reported at 5:08 p.m., the fire was contained within the hour, but smoldering hot spots kept crews busy afterward. Fire investigators remained at the scene.

How it began was still under investigation. There were no preliminary damage estimates available, but Smith said water damage in lower units made the entire building unfit for immediate occupation, he said. The Red Cross was helping people find accommodations.