Chevron Corp has said the fire at its Richmond refinery in the US state of California was contained but not yet extinguished.
"It has been fully contained, but it is not yet extinguished," Chevron spokesman Sean Comey said on Tuesday.
A massive fire broke out in the main processing unit at Chevron Corp's large Richmond refinery, spewing large flames and prompting authorities to order nearby residents to remain indoors.
The fire broke out on Monday evening local time at the 245,000 barrel per day (bpd) plant, which accounts for one-eighth of the state's refining capacity.
Local media and a filing to state regulators, said the fire hit the plant's crude distillation unit.
Another Chevron spokesman Walt Gill told local television that the fire had started in the No. 4 crude unit at 6:15pm local time (01:15 GMT on Tuesday). The size of the No. 4 unit was not immediately clear.
We are "very disappointed that this happened, and apologise that we are inconveniencing our neighbours," Gill said.
Refinery sources said all workers at the plant had been accounted for. There were no injuries reported.
KTVU-TV reported a large blaze was raging at the refinery sending a plume of black smoke into the air over the San Francisco Bay-area plant.
Nearby residents are being told to shelter in place, an order typically given to prevent the risk of exposure to dangerous chemicals.
Sulfuric acid and nitrogen dioxide were released during the incident, according to a filing with the California Emergency Management Agency.
Randy Sawyer, an environmental health officer at Contra Costa County 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,” Sawyer said.
Any prolonged disruption in production could also have a significant impact on the regional fuel markets, particularly gasoline, due to the difficulty in making California's super-clean specifications and the fact that the West Coast region has few immediate alternative supply sources in case of an outage.
The crude distillation unit (CDU) is at the heart of the refining process, converting the crude oil coming into a refinery into intermediate feedstock for all other units.
It can take months to repair a CDU at a large plant, during which time operations are typically severely limited.
As the fire raged in California, a deadline passed on Monday night for an Ecuador court order requiring Chevron to pay $19.04bn in damages in the country’s Amazon region.
The lawsuit was filed in 1993 in a US court and alleges that Chevron had polluted rainforests and waterways and caused birth defects and other injuries to indigenous communities.
Ecuador Judge Liliana Ortiz signed an order Friday giving the oil giant a deadline of midnight Monday to pay the fine or risk having its assets in the country seized.
Andrew Miller is the Washington Advocacy Coordinator for Amazon Watch, told Al Jazeera on Monday that Chevron is unlikely to pay the fine but that the plaintiffs will continue the legal battle.
“You have to understand Chevron earns $85 million a day in profits, so they have the world’s best lawyers, the world’s best lobbyists, and they have the best PR firms,” Miller said.
“But what they don’t have is the moral authority that the plaintiffs on the ground – who are suffering health impacts, who are suffering cancer, they have the moral authority to continue.”