The one-alarm fire was reported at 5:15 a.m. on the third story of a three-story apartment building in the 3200 block of Telegraph Avenue, fire Battalion Chief Emon Usher said.
Firefighters arrived four minutes later and encountered debris and trash throughout the first two floors of the building, making it difficult for them to get to where the fire was on the third floor, Usher said.
Firefighters discovered the rear stairwell on the third floor of the building had burned through. They eventually got to the third floor where they discovered the pot grow operation, he said.
The blaze was controlled by 5:59 a.m., according to Usher.
He said no one was injured, and no one was found in the home. When firefighters forced entry into the front door of the building, a dog ran out. The dog was uninjured.
"It ran to the street corner and looked back like (it was saying) 'Thank you,'" Usher said.
He said police are investigating whether the marijuana grow operation is legal, which depends on how many plants were growing.
Fire investigators are working to determine what sparked the blaze. They are ruling out an electrical cause, and have not found anything suspicious, according to Usher.
He said a possible cause is a candle that was found to have burned down to the bottom of the stick.