A woman was killed in an explosion that rocked an Aliso Viejo medical office building Tuesday afternoon.
Authorities called the explosion suspicious but did not reveal many further details. Both federal and local investigators were on the scene.
Two law enforcement sources told The Times the explosion was likely caused by a package that was delivered to the location, but cautioned that it would be speculative to say the blast was intentional. Local authorities are leading the investigation.
At least one person died inside the building and three others were injured, said Tony Bommarito, a spokesman for the Orange County Fire Authority. The explosion occurred about 1:10 p.m.
"We're trying to determine if a vehicle was involved or if it was an accident or inside the building," said Orange County Sheriff's spokeswoman Carrie Braun.
Bommarito said the county's bomb squad and hazardous materials team were preparing to search the building. He said officials had cleared all the buildings but had not determined if a gas leak caused the explosion.
Orange County Sheriff's Cmdr. Dave Sawyer said it was too early to determine whether the explosion was a bombing, and that investigators were interviewing the three victims who had been transported to hospitals.
The explosion shook the two-story building so forcefully that employees at neighboring businesses thought it was an earthquake. Some stepped outside anticipating more shaking.
Andrew Dyjak, the owner of a massage business inside the building at 11 Mareblu, said he realized it wasn't an earthquake when he got outside and saw the devastation.
"There was one part of the building that was destroyed, like really destroyed," he said. "No windows, glass, and we noticed a small fire."
Glass was everywhere and part of the building's walls looked damaged, Dyjak said.
"For sure we are closing for the day," he said. "I don't think anybody is planning on going back. And they probably have to check the structure."
Besides Dyjak's business, the building also housed at least one chiropractic office and a medical practice, he said.
Laguna Niguel retiree Judith Hoel was sitting in a dental chair inside the Ocean Valley Dental Center across the street from the building, about to get her teeth cleaned, when she heard a "huge boom" and the clinic shook.
"It's terrible to say, but I hoped it was an accident and not something that would be worse," she said. "It's a frightening world today."
More than 30 bystanders stood across the street from the building Tuesday afternoon, snapping selfies and posting updates on social media. Several dozen employees who worked in the medical complex sat in grassy areas facing the office.
Rows of emergency vehicles blocked the streets as a helicopter hovered overhead.
Augustine Tolar had been driving to lunch along Moulton Parkway, passing Oso Parkway, when the explosion caused him to stop.
"I knew right away there would be a fatality. No way in hell could someone survive that big of a hit," said the customer service clerk from Laguna Niguel.
Times staff writer Alene Tchekmedyian and Richard Winton contributed to this report.
11:25 p.m.: This article was updated with information from two law enforcement sources.
8:15 p.m.: The article was updated with information from a news conference.
4:10 p.m.: The article was updated with comments from a witness of the explosion.