"It was like something out of an old horror movie," said Alameda police Detective Sgt. Ron Jones, the head of the vice and narcotics unit.
Twelve plants were inside the room, which featured a separate area for cultivating younger plants, police said.
The room also had automatic lighting, watering and insecticide systems.
The fire at the shed in the 100 block of Cypress Street Thursday caused minimal damage and was extinguished within minutes. What caused it was not immediately clear.
Police were called after a firefighter broke a window to help put out the fire and saw the plants inside the shed, which was converted into a living space.
Investigators later found the bookshelf door while trying to get access to the plants.
No one was home and police said the case remains under investigation.
The discovery of the hidden room came just a day after police arrested a couple on suspicion of growing 10 marijuana plants in the kitchen of their studio apartment in the 700 block of Lincoln Avenue.
Both Catrina Danielle Cuestas, 20, and Ahmad Tariq Hadi, 23, face charges of cultivating marijuana and possessing it for sale.
Hadi denied growing the marijuana to sell, however, showing officers his medicinal marijuana card and telling them he uses the drug to treat insomnia and an eating disorder, according to police.
But police said having a medicinal marijuana card still does not allow someone to grow the drug.
Officers secured a search warrant after neighbors told police the apartment attracted a lot of foot traffic and they suspected drug dealing was going on.
Along with the 10 plants -- each about 1 foot tall -- investigators said they found a scale and packaging materials.
"If you compare the size of the apartment to the size of the grow, it was pretty significant," Jones said.
