Flames engulfed the building, shooting into the air. Commuters could see the flames and smoke from the freeways.
Firefighters were forced to cut into the building to get inside to fight it. Then, part of the building facade collapsed onto a firefighter. He broke his leg and suffered second degree burns.
"A warehouse fire is a dangerous fire depending on what the combustibles are burning inside as well as the complexity of this fire and trying to get around it and suppressing it," said San Francisco Fire Department Lt. Ken Smith.
The owners of the Doggie Daycare in the building next door evacuated some of the pets under their care. But their facility was not damaged.
No explanation yet on why arson investigators have been called to the scene.