She and the three injured were likely in close proximity to the explosion, Sawyer said.
A woman who was on her way to an appointment in the area told CBS2 she arrived just after the blast occurred, and she saw fire on the roof of the building.
He also said that the police finds out causes of the explosion.
The fire at the building at 11 Mareblu - an outpatient medical clinic - was quickly doused following the roughly 1:10 p.m. explosion, but hazardous materials officials and bomb squad investigators were at the scene trying to assess the situation and ensure there was no further danger, Orange County Fire Authority Capt. However, authorities will continue to investigate possible terrorism out of caution.
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. No children were hurt, officials said.
Nothing indicates there were any threats made before the blast, which appeared to be concentrated in a suite on the first floor of the office building, Sawyer said. Tony Bommarito, a spokesman for the Orange County Fire Authority.More news: Judge rules Mueller has authority to prosecute former Trump campaign chairman Manafort
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Investigators are considering the incident as an intentional act, due to the size of the explosion.
Mary McWilliams told the Orange County Register that she arrived for an appointment to find smoke surrounding the area and auto alarms going off.
Bomb technicians are inside the medical building in Aliso Viejo, which was undergoing a renovation, to determine the cause, officials said.
McWilliams says she saw two women covered in ash and soot stagger out of the building.
One woman, who had skin peeling on her arm from burns, said, "Take care of my mother", McWilliams said. No children were injured, officials said.
Bommarito said one of the injured people suffered from smoke inhalation, but the extent of the other victims' injuries was unknown.