WATCH LIVE: At least 14 dead in mass shooting at San Bernardino social services agency

As many as 28 people have been shot at a social services facility in Southern California.

Police are seeking one to three heavily armed men -- who were wearing masks, military-style clothing and possibly body armor -- after a mass shooting at Inland Regional Center in San Bernardino.

Police chief Jarrod Burguan said in a press conference that up to 14 people were killed in the shooting, and at least 14 others were wounded. Police do not have a motive for the shooting. "These are people that came prepared" and were armed with "long guns," Burguan remarked.

"Obviously at minimum we have a domestic terrorism type situation that occurred here... They came prepared to do what they did, as if they were on a mission," he added.

Emergency crews were called about 11:30 a.m. local time to the shooting scene in the 1300 block of South Waterman Avenue. The gunmen are believed to have fled the scene in a black SUV.

A bomb squad was sent to dismantle a possible explosive device.

Initial reports suggested the shooting happened near a Planned Parenthood clinic. The shooting happened several blocks away, and employees there said the clinic was not a target.

The Inland Regional Center has 650 employees and serves the developmentally disabled.

“There would be family members and persons with developmental disabilities there for appointments such as with their case manager or for evaluations, etc.” Eileen Richey, executive director for the Association of Regional Center Agencies, told The Sun.

A spokeswoman for the medical center said the shooting took place in a conference room that had been rented Wednesday to the San Bernardino Department of Public Health.

Police were reportedly conducting a training exercise nearby and were able to respond quickly.

The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives are assisting local law enforcement in the investigation.