Flames were shooting from a warehouse on Brook Street. Cans of food stored on the upper floor were exploding, but that's not what got police involved.
On the ground floor, firefighters discovered a large illegal marijuana growing operation -- nearly 500 plants, an elaborate lighting grid and a ventilation system to filter away any pot odor.
It is the second time this week that fire crews have stumbled upon a major marijuana growing operation in the East Bay. A fire in Richmond led to the discovery of another pot growing operation three days ago.
Neighbors were none the wiser.
"We knew nothing about this. We would walk by this and we'd see nobody going in or going out. It's pretty amazing. It's like a grow room gone wrong," said Oakland resident Simone Young.
Other neighbors recall seeing what they thought were people moving restaurant equipment in and out.
Hojoon Kang said, "They were not here often either. They were here late at night maybe once or twice a month."
Inside, firefighters discovered wiring that apparently powered the marijuana growing operation, which presented challenges when they started their attack.
"When you have a large growing operation, you don't know how they're getting their electrical source. And so we have to be mindful of that so we had PG&E come out and cut off electricity to both buildings immediately," said Battalion Chief Emon Usher of the Oakland Fire Department
Oakland firefighters have been to the location where the marijuana plants were discovered in the past with tragic results. In 1999, firefighter Tracy Toomey was killed when flames tore through a bar on the Broadway side.
There were no injuries Saturday morning.
Oakland police pulled out a few marijuana plants in the afternoon, but were waiting for the water to stop dripping from the top floor before finishing the job.
The fire apparently started on the top floor where there was some type of food warehouse. At this point investigators don't know if the electrical system for the marijuana facility was a factor.
Police have been in contact with the building's owner, who has been cooperative. They're now trying to track down the people who signed the lease.