Carrie Braun, a spokeswoman with the Orange County Sheriff's Office, said: "We are still trying to determine if this explosion was accidental or intentional". Authorities say one person is dead and several others have injuries. One of those three suffered smoke inhalation.
Officials are unclear what led to the explosion, but are not ruling anything out.
Authorities had not found an explosive device Tuesday night but were searching through debris that was left after the blast.
The official, who was briefed on the investigation, was not authorized to discuss the matter publicly and spoke to The Associated Press on condition of anonymity. The blast caused extensive damage to buildings in the area, Sawyer said.
Officials reportedly said the person who died is a woman and was near to the source of the explosion, The Orange County Register reported. Some reports indicated the building may have been under construction work at the time. There were early reports that a vehicle had crashed into the building, but that turned out not to be the case.
There's no "initial indication" of terrorism right now, Mike Gifford, spokesperson for Federal Bureau of Investigation in Los Angeles, said.
"The investigation is ongoing", Braun told Xinhua by telephone.
"... They weren't on fire, they were helping each other across the street, walking very slowly and a lot of shock, shaking, just full of ash all over their face, eyes bloodshot, just blood all over", the woman said. OCFA said a bomb squad was sent in to assess the situation and investigate the cause of the blast.
In this photo taken from video provided by KABC-TV, children are evacuated from a preschool across the street from a building that was rocked by an explosion in Aliso Viejo, Calif., Tuesday afternoon, May 15, 2018. Babies were seen being wheeled out of the facility in cribs, and toddlers held hands with each other and firefighters as they walked to a nearby Target for safety.
Emergency services have closed the westbound carriageway of Pacific Drive.
Retailer Gap says 'sorry' for T-shirt's incorrect China map
Other T-shirts in the range show San Francisco, Paris, Japan and Canada but are decorated with national flags rather than maps. The Global Times quoted Gap as saying that the T-shirt had not been released in China.