Late Tuesday afternoon, NBC4 - citing unnamed federal sources - said investigators had determined that the blast was an "intentional detonation", and the explosive device was delivered to the building, addressed to a specific person. It blew siding off the walls, exposing insulation and framing and shattering windows at the two-story building.
A United States official told the Associated Press the authorities were investigating it as an intentional act and a package may have caused the blast.
Authorities had not found an explosive device Tuesday night but were searching through debris that was left after the blast.
A daycare and preschool are near the site of the explosion, but authorities said all of the children are safe.
"The corner of that building, the whole bottom floor is pretty much blown out", fire Capt.
A third person suffered smoke inhalation, fire officials said. She and the three injured were likely in close proximity to the explosion, Sawyer said.
Bomb technicians from the Orange County Sheriff's Department, the Federal Bureau of Investigation and other agencies were investigating, said Paul Delacourt, the assistant director in charge of the FBI's field office in Los Angeles.
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Orange County Fire Authority Chief Brian Fennesy said they received a call around 1:09 p.m.
Officials originally believed the explosion was caused by a vehicle crashing into the building, but Orange County Sheriff's Department spokeswoman Carrie Braun said no auto was involved and the department was investigating how the explosion occurred.
"Take care of my mother, take care of my mother!" shouted one woman as she fled, according to NBC4. Other people could be seen wheeling cribs down the street as the area was evacuated.
Authorities said they are not actively seeking a suspect.
There were unconfirmed initial witness reports that the blast may have been a gas explosion, but Bommarito said it is rare for such gas-fueled blast to occur in a commercial building. The other woman was burned and her head was bleeding.
"The survivors' injuries were consistent with an explosion, but not necessarily consistent with a bomb".