Chevron Corp. crews on Thursday were working to purge natural gas from a 12-inch diameter pipeline after a fire erupted in an underground gas storage area Wednesday night, forcing thousands to be evacuated from the East Bay near Oakland.

An evacuation order remained in place Thursday afternoon for about 4,000 people from nearly 1,400 homes in the Bay Point and Pittsburg areas, which are about 30 miles northeast of Oakland, after the gas storage area caught fire near a pipeline in Bay Point, according to the Contra Costa County Fire Protection District (FPD). As of Thursday afternoon, there was no threat of an explosion and the impacted line had been isolated from other pipelines, officials said.

According to Chevron, the company was contacted about 8 p.m. Wednesday about the incident on the high-pressure pipeline, which runs through the East Bay.

“Chevron Pipe Line Co. (CPL) was notified of a fire caused by a Pacific Gas and Electric Co. (PG&E) power line falling, which started a fire near our valve junction on the Northern California Gas Line near Pittsburg,” it stated. “CPL immediately shut down the line and dispatched a field team to investigate.”

The California Public Utilities Commission (CPUC) said it was investigating the incident, and a PG&E utility spokesperson told NGI that its crews continue to assist first responders at the site and 22 customers remained without electric service in the afternoon Thursday. He said the cause of the incidents were still under investigation, and PG&E could not determine if the Chevron and earlier electric line fires were connected.

Chevron was injecting nitrogen to extinguish the fire, according to the Contra Costa FPD. An entry team was at the site Thursday afternoon, with an initial assessment pending.

According to officials, a grass fire erupted about 6 p.m. on Wednesday night near the pipeline, which was extinguished by the FPD. However, about an hour later, a second fire was reported in a nearby underground vault that serves as a storage unit for the pipeline.

The FPD determined there was a “high probability of danger” following the underground fire, which led to requests for people to evacuate homes within a half-mile radius of the pipeline.

The Pittsburg Police Department used drones to keep infrared eyes on the gas pipeline Wednesday night, which allowed the FPD to track temperatures in the vault.

Evacuation centers were opened and area schools were closed on Thursday. No injuries had been reported.

“Venting of the Bay Point gas line is resulting in a loud, shrieking noise that has been described as a jet-engine-like sound emanating from the Chevron Pipeline Facility on Buchanan Road in Antioch,” Contra Costa FPD tweeted. “This is a normal part of the risk-mitigation process.” Residents were urged to not call 911.