(CNN) -- All Terry Pettit could do was worry as he stood near the offices of the Inland Regional Center in San Bernardino, California.
News of shootings at the agency for people with developmental disabilities was spreading fast -- with possibly 20 victims -- and all Pettit knew about his daughter inside the building came from her text messages on his cell phone.
"Shooting at my work. People shot."
"Pray for us. I am locked in an office."
Pettit wept for his daughter as he spoke with reporters. Sirens blared in the background.
"She's been hiding," he said.
Details of yet another mass shooting trickled out slowly.
'They came prepared'
San Bernardino Police Chief Jarrod Burguan told reporters Wednesday afternoon that gunmen had killed at least 14 people and wounded at least 14 others.
David Bowdich, assistant director of the Los Angeles FBI office, said it was not known whether terrorism was the motive.
Burguan said the shooting was, "at a minimum," an act of domestic terrorism.
The shooters came with long guns, Burguan said.
"They came prepared to do what they did, as if they were on a mission," he said.
Witnesses told police they saw three men with long rifles, a law enforcement source said. The three men got into a black SUV and drove away, the source said, citing the witnesses.
After a SWAT team cleared the building, a sheriff's bomb squad found a suspicious package on the second floor, the source said. An explosive ordnance disposal team determined it is "not normal" and they are going to handle it by robot, the source said.
'We thought it was a fire drill'
The executive director of the Inland Regional Center, Lavinia Johnson, told CNN she believes county health officials were having a holiday event at a conference center where one to three shooters entered and opened fire.
Burguan confirmed that most of the victims were "centrally located in one area of the facility."
But authorities haven't confirmed what type of event was being held.
"I've heard everything that it was a meeting to a potential ... lunch-type gathering, maybe for the holidays," he said.
Johnson said staff and clients remained in locked offices until police arrived.
"As far as we know, we're all OK," she said, adding that center personnel were gathered in groups at a golf course across the street.
Johnson said a fire alarm was activated at the time of the shooting. Some people began evacuating.
"We thought it was a fire drill," she said. "We started to exit. ... We were told to go back into the building."
Some people could still be hiding inside hours after the rampage, she said.
"I'm very concerned about my staff and just want to be sure they get the support they need at this time," Johnson said.
'They've seen bodies on the floor'
Marcos Aguilera told CNN affiliate KABC-TV that his wife had just made it out of the building.
"She said the guy came in next to her office and I guess started shooting," he said. "Then he locked himself in her office. They've seen bodies on the floor."
Aguilera's wife said she saw the bodies as SWAT team members escorted her out.
"She doesn't know if they were deceased or if they had just been shot," he said.
Inland Regional Center's Facebook page says it employs nearly 670 staff at its facilities in San Bernardino and Riverside counties, providing service to more than 30,200 people.
The center aims to "work on a personal, one-on-one basis with people with developmental disabilities to make their lives better as they define it."
On Wednesday afternoon, however, the area surrounding the center resembled a war zone, with dozens of people walking out of the building with their hands in the air and lines of heavily armed officers aiming their weapons. Some of the wounded were taken out on stretchers. Triage stations were set up outside.
Kristin Krause, who works at a charter school about a mile away, said the staff and 400 students were on lockdown.
The students were secure, she said.
"We have all gates locked. We are doing everything we can to make sure our kids are protected."
A facility for the blind that caters to mostly elderly people across the street from the shooting scene also was on lockdown, according to Elizabeth Mendieta, a driver who transports clients.
Wednesday afternoon, SWAT teams and the bomb squad were still working to clear the building complex.