ALISO VIEJO, Calif. -- One person was killed Tuesday and three others injured in an explosion in a medical building in Aliso Viejo, California, authorities said.
It's unclear whether the explosion was intentional or accidental, said Orange County Sheriff's Department Commander Dave Sawyer in a news conference Tuesday.
Authorities cautioned that the investigation was still in its early stage and that they had begun processing the inside of the building.
"We have not found any type of specific device inside of the building right now that would tell us or lead us to exactly what the device was -- if there was a device," Sawyer said.
The identity of the female victim who was killed, has yet to be released. She and the three injured were likely in close proximity to the explosion, Sawyer said. Investigators are interviewing the three injured.
Two survivors had critical injuries "that were consistent with an explosion, but not necessarily consistent with a bomb," said Carrie Braun, a spokeswoman for the Orange County Sheriff's Department.
The explosion blew out walls and windows, heavily damaging the first floor corner of the two-story building and hurling debris outside, said Capt. Tony Bommarito, a spokesman for the Orange County Fire Authority.
Bommarito said there didn't appear to be a gas leak.
At this point, officials are not ruling anything out. The blast caused extensive damage to buildings in the area, Sawyer said.
"Anytime you see an explosion of this magnitude, it would definitely be suspicious to us and that's why we rolled out all the resources to get to the bottom of it," he 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. And there is no specific person that authorities are searching for right now, he added.
FBI spokesman Mike Gifford had earlier said there was no initial indication of terrorism in the facility about 7 miles northeast of Laguna Beach.
The sheriff's department is partnering with the FBI, the Department of Homeland Security, and the Bureau of Alcohol, Tobacco, Firearms and Explosives, who will assist the investigation.
Witness: Felt 'almost like an earthquake'
Firefighters responded to a call of an explosion shortly after 1 p.m. local time.
Dong Shin, a witness, said he heard a loud boom minutes before his appointment in a nearby building.
"And the ground shook," he told CNN. "My whole body shook."
"While the ground was shaking ... my body jolted and my head hit the wall," Shin said.
He said it felt "almost like an earthquake, but a big earthquake."
Shin said he and others hurried down the stairs to get out of that building, and saw "two holes in the wall" of the medical facility.
Shin said he also saw "fire, smoke, insulation popping out of the walls, a lot of scared people running around, a lot of commotion."
He recalled that one woman ran out of the medical building and was escorted to safety. Her face was covered in blood, he said.
"It was big noise and I thought it was a garbage truck," said Kingston Dik, student.
Dik, who is 6 years old and the rest of the students at Academy of the Hills were evacuated. News chopper video showed babies in cribs being pulled out of the daycare by first responders.
Judith Hoell also felt the blast, she was at the dentist's office across the street.
"It was very loud and the building shook and I actually felt it in the dental chair," said Hoell. "It appeared part of the building had a large hole in it and you could see flames."
Tony Dik learned about the incident online and then soon realized it was by his son's school.
"Panic but at the same time you have to keep calm and drive as quickly and safely as possible to get them," said Dik.
Parents who were reunited with their children at the scene described emotions as overwhelming.
"It's like he was born again. You get big tears and give him that hug that you always wanted to," said Dik. "You don’t see this in Orange county or anywhere for that matter or this big of scale. It's pretty freaky."
Aliso Viejo is about 75 miles northwest of San Diego.