The crack was identified Saturday night during a visual inspection of the 7,000-gallon tank at the GKN Aerospace facility in Garden Grove.

Garden Grove is in northern Orange County, about 35 miles southeast of Los Angeles and 4 miles from Disneyland in Anaheim.

The threat of an explosion led to evacuation orders affecting 50,000 people.

Lydia Green, who lives in Anaheim, about a mile from the facility, is one of them.

“I’m feeling nervous, scared, devastated,” Green told NBC News on Sunday at a shelter at John F. Kennedy High School in nearby La Palma. “I’ve been without my medication, my basic needs — food, hotels, we haven’t had a hotel. It’s been very hard.”

She and her partner, Eugene Smith, had been sleeping in their car. Smith described the ordeal as “like living in a nightmare,” and said he feared a devastating explosion and its aftermath.

“Blowing up and then contaminating everything. Everything. That’s where we live at. That’s our home,” he said.

Jaden Gebelein was also at the shelter and said he was nervous, as he lives on the border of the evacuation zone.

“It’s a lot of anger. ... I feel like why there are these facilities right next to a bunch of houses? And it makes me upset, too,” he said. “You hope that it gets managed well and then the worst-case scenario doesn’t happen, because those are people’s houses, and it’s probably going to affect a lot bigger of a radius than they let on.”

The American Red Cross said Monday that more than 1,000 people have been provided emergency shelter at seven shelters. Five of the seven were at or near capacity for overnight stays but were still able to provide meals and other services, it said in a statement listing locations.

Since the risk has been mitigated, the Orange County Fire Authority said on Monday it would re-evaluate the evacuation zones. Officials told people not to return to evacuation zone areas until they was deemed safe.

McGovern, the Orange County interim fire chief, said Monday morning that some of the material is solidifying but officials did not know how much of if some remained in a vapor state.

“We still have a potential for an explosion that’s not as bad as a BLEVE, but it’s still a threat,” McGovern said.

The Environmental Protection Agency has enabled air monitoring at 20 locations around the area, the official said. The Federal Emergency Management Agency has deployed a local officer to coordinate with officials, sent a team to the State Emergency Operation Center and activated its Interagency Modeling and Atmospheric Assessment Center, which models airborne hazards.

Earlier Monday, authorities said that one of three tanks at the facility had been neutralized by introducing a compound into it, but that the other two — including the affected tank — have not.

The Orange County Fire Authority quashed reports that there may be more than one crack on the tank.

“There is also peeling of the weather stripping on the exterior, but this is not an additional crack. There is currently no active leak, and continuous live atmospheric monitoring confirms there are no chemicals leaking,” it said in a post on X.

A spokesperson for GKN Aerospace said Sunday that the company was monitoring the condition of the “affected material” and that crews were working “around the clock to mitigate the risk of a leak.”

McGovern said Sunday that air monitoring has shown the possible fissure has not led to the release of toxic air.

Covey told NBC News that an explosion could set off a blast in a nearby 15,000-gallon tank and a 4,500-gallon tank that also holds methyl methacrylate.

The blast radius, which stretches up to half a mile, would cause severe structural damage and most likely disperse toxic vapors into the air, officials said. They also expressed concern that the tank could rupture and release toxic material into waterways.

“We’re talking about possibly one of the worst chemical incidents in California history,” Covey said.

Concerns about the 7,000-gallon tank first arose Thursday when Orange County fire officials reported a “vapor release” at the aerospace facility. Further investigation found that the tank’s temperatures were rising.

Firefighters used sprinklers and hose lines to cool the tank. McGovern said that during a team operation Saturday night, crews saw that the pin on the temperature gauge was reading 100 degrees Fahrenheit, the highest level it shows, which indicated that actual temperatures in the tank could be higher.

A White House official said Monday that the Trump administration “is engaged and monitoring the situation.”

Gov. Gavin Newsom declared a state of emergency in Orange County on Saturday.

President Donald Trump signed a federal emergency declaration, which allows for greater aid, Newsom and U.S. Rep Derek Tran, D-Calif., said Monday.

“This new federal assistance will further bolster our resources to help resolve this situation,” Newsom said in a statement.

Steve Patterson and Shanshan Dong reported from La Palma, Marlene Lenthang from Los Angeles and Aria Bendix from New York.