ALISO VIEJO (CBSLA) – At least one person was killed and three others hurt in an explosion and fire at a medical building in Aliso Viejo Tuesday afternoon.

The explosion was reported at around 1:10 p.m. at a two-story outpatient medical clinic located at 11 Mareblu. Following the explosion, all surrounding buildings were evacuated.

A federal official who spoke to the Associated Press on the condition of anonymity late Tuesday said the incident was being investigated as an intentional act and that the blast may have been cause by a package.

However, officials reported earlier that no device had been found at the scene.

“We have not found any type of specific device inside of the building right now that could tell us or lead us to what exactly the device was, if it was a device,” said Cdr. Dave Sawyer with the Orange County Sheriff’s Dept. at a Tuesday night press conference.

According to the Orange County Fire Authority, the explosion occurred on the first floor inside the building.

One person was confirmed dead on scene and three others have been hospitalized.

Authorities said the victim was a woman but did not release her name.

At least two of the people injured were taken to local trauma centers, said OCFA Capt. Tony Bommarito. The nature and extent of their injuries were not immediately known.

Initial reports indicated a vehicle may have also crashed into the building, but authorities later said that no vehicle was involved.

A Sheriff’s Department bomb squad and OCFA hazmat team were on scene. Later in the day, ATF, FBI and Homeland Security officials were on scene as well to assist with the investigation.

Authorities were trying to determine the best way to search the building, which officials say appeared to be undergoing some type of construction.

Sheriff’s deputies were seen taking photos of license plates for all vehicles leaving the area, CBS2’s Michele Gile reported.

“The plan right now is kind of a holding pattern,” Bommarito said. “We’re basically going to our hazmat team and the bomb squad together, they’re gonna form a plan, have a conversation, and see the best way to assess the situation before we start putting our guys inside.”

Children from neighboring Academy on the Hills, a Montessori private preschool located at 10 Mareblu, were evacuated from the building, some of whom were still being transported in their cribs. Officials say no children were injured.

Parents were asked to pick them up in the parking lot of the nearby Target store on La Paz Road.

“We just saw them walk across, and I know they couldn’t get them out because of the gas leak and everything, too, so we’re still kind of wondering what all went wrong,” said one mother.

“Little nervous and concerned that something else bigger was happening. I think, just in this day and age, with things that kind of go on, just definitely pretty careful, but trying to stay calm and knew that she was in really good hands,” said another parent.

Eastbound Pacific Park Drive was closed from Mareblu to the Aliso Plaza. Westbound Pacific Park Drive was also shut down from Mareblu to Moulton Parkway. People were also asked to avoid Oso Parkway and La Paz Road.

This is a breaking news report. More information will be provided as it becomes available.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. City News Service contributed to this report.)ted. Wire services contributed to this report.)