California: The authorities in Southern California were scrambling on Friday to prevent a potentially catastrophic explosion at an aerospace plastics facility after a hazardous chemical leak triggered evacuation orders affecting nearly 40,000 residents across parts of Orange County.

The emergency began Thursday when a storage tank containing between 6,000 and 7,000 gallons of methyl methacrylate, a chemical commonly used in the production of plastic components, overheated and started releasing vapours into the air at a GKN Aerospace facility in Garden Grove.

Officials warned that the tank could rupture or explode if conditions worsened.

“This thing is going to fail, and we don’t know when,” Orange County Fire Authority Division Chief Craig Covey said. “We’re doing our best to figure out when or how we can prevent it.”

Evacuation orders initially issued for residents in Garden Grove were later expanded to include parts of Cypress, Stanton, Anaheim, Buena Park and Westminster after crews failed to contain the leak overnight.

The authorities said no injuries or fatalities had been reported.

Later on Friday, Covey said crews had managed to stabilise the tank’s temperature temporarily, giving emergency teams more time to assess how to safely neutralise the threat.

Garden Grove, located around 38 miles south of downtown Los Angeles, sits less than a mile from Disneyland Resort, though the theme parks were not included in the evacuation zone.

Resident Danny Pham said he woke up to the emergency only after his roommate urgently alerted him on Friday morning.

“It was shocking to me,” said Pham, who lives only a couple blocks from the plastics plant. “I didn’t know how serious it would be. I never knew that a thing like this could happen.”

Pham said he fled with only his wallet and passport before taking shelter at a friend’s restaurant in a neighbouring city. By Friday evening, he was still unsure where he would spend the night.

The authorities have also built containment barriers using sandbags to stop any chemical spill from entering storm drains, nearby creeks or the ocean.

Orange County health officer Dr Regina Chinsio-Kwong warned that heated methyl methacrylate can release dangerous vapours capable of causing respiratory problems, eye irritation, nausea and headaches.

Emergency crews were able to stabilise one of the two affected tanks earlier, but officials later identified the second tank as posing the greatest risk.

GKN Aerospace said specialist hazardous-material teams were continuing to evaluate the situation.

“There are no reports of injuries at this time, and our priority remains the safety of our employees, responders, and the surrounding community,” a company spokesperson said in a statement. “We will provide verified updates as soon as more information becomes available.”

Another Garden Grove resident, Kim Yen, said she received an evacuation alert on her phone Thursday night while preparing for bed.

“They are family,” she said of concerns for members of the city’s large Vietnamese community who may not fully understand English-language alerts. “I’m hoping they stay alert and listen to the news and the authorities. This is scary.”

Yen later returned briefly to collect medications and important documents, describing her neighbourhood as “a ghost town” after the evacuations.

“We understand that this is frightening,” Garden Grove Mayor Stephanie Klopfenstein said. “But the evacuation orders are in place for your safety.”