The blaze was reported at an outbuilding next to a building housing a Western Roofing Supply business on Lonus Street near Lincoln Avenue around 11 a.m., San Jose Fire Capt. Mike Van Elgort said.
Crews arriving on the scene saw heavy fire coming from a small outbuilding attached to the roofing supply business building.
The flames quickly spread from the smaller building to the main commercial building and a second alarm was called, Van Elgort said.
Firefighters got the fire under control around 12:20 p.m., the captain said.
The blaze displaced one person living in the outbuilding, and the American Red Cross was called to provide housing assistance.
Van Elgort said investigators believe the fire may be suspicious but have not yet determined a cause.
No injuries were reported in connection with the blaze and a damage estimate was not available.