The first call came in at 2:39 p.m. and the fire quickly elevated to a second and third alarm.
The blaze, clearly visible from Highway 4, was driven by the wind and spread to a structure at the business and then ignited grass across the nearby abandoned train tracks.
Here are photos from @ContraCostaFire of the aftermath of the fire at the Elite Roofing Supply Company. An official says the fire started at the homeless encampment just north of this yard #Pittsburg pic.twitter.com/B2MJxeYVLQ— Liz Kreutz (@ABCLiz) June 24, 2019
A huge plume of smoke was visible, a spokesman said.
Contra Costa Fire officials say that one firefighter has been injured and transported to the hospital. He's currently being treated for smoke inhalation and will likely be released Sunday night.
Fire officials also said the fire was started at a nearby homeless encampment, then made its way to the Elite Roofing Supply company.
They say a "very high" number of grass fires start in or near homeless camps.
Bay City News contributed to this report.