The first fire was reported at 6:13 a.m. at 1427 Mendell St. in the city's Bayview District, where firefighters responded and found a suspected marijuana grow house, the fire official said.
The fire was contained at 6:32 a.m. and the circumstances of the grow operation remain under investigation.
At 6:21 a.m., another fire was reported at 562 Banks St. in Bernal Heights. Firefighters responded and contained the blaze to the front porch of the home, the fire official said.
A third fire was also reported at 6:29 a.m. at 215 Ney St. in the city's Excelsior District. That blaze was extinguished at 7:08 a.m., according to the fire official.
No injuries were reported in any of the three fires.