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(CNN) —  

The deadly explosion in an Orange County building that killed one woman and injured three others appears to be intentional and is being investigated as a criminal act, a law enforcement source told CNN.

But the source also cautioned that it’s early in the investigation.

The Orange County Sheriff’s Department stated in response to news reports: “Despite media reports quoting unnamed sources, we have not confirmed that the explosion is intentional, nor have we conclusively identified the source of the explosion. Investigation is in early stages, as information is confirmed we will share it.”

The explosion rocked a medical building in Aliso Viejo, California, on Tuesday. It 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.

In a news conference Tuesday night, Orange County Sheriff’s Department Commander Dave Sawyer said it was unclear whether the explosion was intentional or accidental.

The investigation is still in its early stage and authorities had begun processing the inside of the building, he said.

“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.

Bommarito said there didn’t appear to be a gas leak.

The blast, which erupted around 1 p.m (4 p.m. ET), caused extensive damage to buildings in the area, Orange County Sheriff’s Department Commander Dave Sawyer said earlier.

“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,” Sawyer said earlier.

Nothing indicates there were any threats made before the blast, Sawyer said.

FBI spokesman Mike Gifford had said earlier there was no initial indication of terrorism in the facility about 7 miles northeast of Laguna Beach.

The FBI, the Department of Homeland Security and the Bureau of Alcohol, Tobacco, Firearms and Explosives are assisting investigators.

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.

CNN’s Paul Vercammen, Joe Sutton, Madison Park and Dave Alsup contributed to this report.