SAN FRANCISCO (CBS SF) — An early morning fire displaced seven people and damaged a four-story apartment building in San Francisco’s Twin Peaks neighborhood Thursday, fire officials said.

Firefighters responded to the one-alarm blaze at about 2:10 a.m. at Glendale and Market streets.

READ MORE: Long Lines Form Outside San Mateo Event Center COVID-19 Vaccination Site

Crews were able to extinguish the fire within about an hour, according to fire officials.

One person suffered injuries not considered life-threatening and they were taken to a hospital.

Residents on the first and second floor were able to return to their units, but the third floor is without power and a unit on the fourth floor sustained extensive damage, fire officials said.

READ MORE: Late Rally Fizzles, Warriors Fall to Spurs 112-107

In all, an estimated 21 people were affected by the blaze.

The American Red Cross and city departments are assisting the affected residents. A resident who uses a wheelchair was able to stay with a neighbor and is contacting On Lok Lifeways, which provide services for senior citizens.

Fire investigators are looking into what caused the blaze.

MORE NEWS: King Tide Flooding on SF Waterfront Foreshadows Future Climate Change Norm

© Copyright 2018 CBS Broadcasting Inc. and Bay City News Service. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.