Dispatchers received report of a fire at 5:47 p.m. on the second floor of a three-story apartment building at 35 Dolores Street, between Market and 14th streets.
Crews arrived on scene at 5:50 p.m. to find smoke coming from the building and heavy flame in the attic.
As of 6 p.m. the roadway out front had been blocked off and firefighters had extended ladders up to the building's exterior.
According to some reports, the fire has been brought under control.
No injuries had been reported at that time, according to firefighters. Further details were not immediately available.