There were unconfirmed reports that a vehicle may have also crashed into the building, OCFA said.
The crash was reported around 1 p.m. Tuesday in the 5 block of Mareblu in Aliso Viejo off of Route 73, the Orange County Fire Authority confirmed.
The fire has been put out but a bomb squad and a hazmat team remained at the scene to assess the area's safety, Bommarito said.
The FBI was sending resources to the scene, but agency spokesperson Mike Gifford said there was no early indication of terrorism, CNN reporter Kristen Holmes tweeted. The three people who were injured were nearby and were being questioned by investigators late Tuesday night, he said.More news: Whole Foods sales items get even cheaper for Amazon Prime members
"As far as what I'm hearing there was no auto involved", Carrie Braun of the Orange County Sheriff's Department said. Mr. Bommarito said all three were expected to survive.
Dong Shin, a witness, said he heard a loud boom minutes before his appointment in a nearby building.
Federal, state and local authorities, including the FBI and the Department of Homeland Security, are investigating the blast, which occurred on the first floor of a building that was under renovation. The official said the information was based on a preliminary investigation.
Officials originally believed the explosion was caused by a auto crashing into the building, but Orange County Sheriff's Department spokeswoman Carrie Braun said no vehicle was involved and the department was investigating how the explosion occurred.More news: Pakistan top brass blast ex-PM over Mumbai attack remarks
Little children holding hands and others being pushed in rolling cribs were led by firefighters to a Target parking lot to be united with parents. It was not immediately clear what prompted that call.
The injured were taken to a hospital and there's no immediate word on their conditions.
"Then everyone started running out of buildings everywhere with looks on their faces of just horror", the woman said.
McWilliams says she saw two women covered in ash and soot stagger out of the building. The other woman was burned and her head was bleeding.More news: Mile Jedinak one game from Premier League return with Aston Villa