Among the injured were a 40-year-old man and a 36-year-old women who are being treated for burns.
The fire broke out just after 6:50 p.m. on Wednesday. It's burning a three-story building near 22nd and Mission streets.
Firefighters are taking a defensive position and are letting the building burn.
Witnesses have reported of seeing people escaping from the building on fire escapes and and coughing and suffering from smoke inhalation.
The mixed-use building has businesses and office buildings on the first and second floor and the third floor is mostly residential.
Mission Local, a San Francisco blog, reported that their office is in the building that caught fire.
Everyone in ML staff is OK and reporting on scene. Unclear how many injuries there are in bldg. More updates coming: http://t.co/4IqOM9atP9— Mission Local (@MLNow) January 29, 2015
Smoke is covering the entire west side of Potrero Hill, according to one resident.
News crews and onlookers being moved back as for continues to creep toward Mission corner from 22 side pic.twitter.com/Jujtavt5s2— Mission Local (@MLNow) January 29, 2015