"We have not determined what caused the blast", said Carrie Braun, a Public Information Officer at Orange County Sheriff's Department.
A USA official says a deadly explosion at a Southern California office building is being investigated as an intentional act and investigators believe the blast may have come from a package.
The official was briefed on the investigation but wasn't authorized to discuss the matter publicly and spoke to The Associated Press on condition of anonymity.
Mary McWilliams of San Clemente tells the Orange County Register that she saw two women with burns stagger out of the building.
Authorities were not searching for any specific suspects Tuesday night, but the investigation was continuing, he said.
A third person suffered smoke inhalation, fire officials said.
"We are trying to understand was the explosion an accident or an explosive device went off", said Pennesi.
The head of the local fire Department Brian Pennisi also noted that two people were injured, reports CNN.
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Investigators are considering the incident as an intentional act, due to the size of the explosion.
That building is located at 11 Mareblu, OCFA tweeted. McWilliams says one woman had skin peeling on her arm.
He said the person who died was inside the building when the blast occurred.
"... 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.
The county's bomb squad and a hazmat team are preparing to search the building where the explosion occurred. The cause of the blast is being investigated. The injured were taken to a hospital. No children were injured, officials said.
A day care center nearby was unaffected, but working to reunite parents with their children.
It wasn't immediately clear how many people were hurt, but authorities said there were at least two patients transported.