The fire was first reported at about 1:45 p.m. on Boggs Avenue, Fremont Battalion Chief Rich Dickinson said.
The building houses a small machine manufacturing plant. The fire department says that due to the nature of the business they are concerned there may be flammable materials inside.
Fremont Fire Capt. Steve Silva is encouraging surrounding businesses and residents to shelter in place and shut down HVAC systems. He says this is the biggest fire they've seen "in a while."
Nearby businesses have been evacuated. There are no reports of injuries.
The Fremont Fire Department, Fremont police and the California Highway Patrol are on scene.
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