According to media reports, the fire started in the oil refinery's No. 4 crude distillation unit at 6:15 pm local time on Monday (01:15 GMT Tuesday).
Towers of black smoke and huge flames were seen issuing from the fire, as fire fighters struggled to bring it under control.
Local sources say that all of the facility’s workers have been accounted for and no injuries have been reported.
However, residents have been warned by officials to stay indoors, as toxic sulfuric acid and nitrogen dioxide fumes have been released by the fire.
Ryan Lackay, a 45-year-old employee at a chemical plant next to the refinery said, "I walked outside and saw what looked like a lot of steam coming out of Chevron, way more than usual. I thought they must have blown a boiler."
"And then all of a sudden it just went whoosh, it ignited," he added.
Randy Sawyer, an environmental health officer at Contra Costa Country Health Services told Al Jazeera
, that “The biggest concern is the smoke."
“All kinds of smoke are toxic and there are a lot of particulates in the smoke, so we’re all asking people to shelter in place ... to go inside shut their doors and windows. Keep the outside air, the smoke, from going inside your home.
“Particulates can cause people to have breathing problems … and if there are any gasses in [the smoke] there could be other problems especially for [people with] pre-existing conditions like emphysema or asthma,” he added
Spokesperson for the 245,000 barrel per day refinery, Walt Gill, told local media that it was unknown when the fire would be completely extinguished. He described the incident as a "disappointment" and apologized for “inconveniencing our neighbors.”
Chevron spokeswoman, Heather Kulp, told local media that an investigation is currently underway to ascertain the cause of the fire. She said that crews were looking into a fuel leak that occurred in the facility immediately prior to the blaze.
The No. 4 crude distillation unit (CDU) is of paramount importance to the oil refinery process and significant damage could take months to repair.
are being voiced of an increase in local oil prices if the facility is shut down for an extended period.
Pavel Molchanov, an analyst with investment firm Raymond James told the Marin Independent Journal
, "If the refinery is disrupted for an extended period of time, there would be an effect on gasoline prices on the West Coast. The effect on California fuel prices is likely to be meaningful."
A lengthy disruption in production could also have an effect on the fuel supply in the West Coast, and the region apparently has few immediate alternative supply sources.
Bob van der Valk, a petroleum industry analyst in Terry, Montana, told Reuters
, "Chevron will have a hard time finding replacement barrels in an already short market."
"Refineries are already drawing down summer blend inventory in anticipation of the switch back to winter blend gasoline."