A man and a woman suspect wearing combat-style clothing were killed in a gunfight with police hours after they fled from the shooting site in a SUV.
The mass shooting took place inside a packed conference room located within Inland Regional Centre in San Bernardino which assists people with developmental disabilities.
Hundreds of people were evacuated from the health care centre as police officers swept through the massive complex and into the residential area. Others locked themselves in rooms waiting for police to arrive.
He said it was not clear if the person was involved in the massacre. He also said there still might be a suspect at-large, and searches were continuing in the city 60 miles east of Los Angeles.
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One of the suspects in the shooting has been identified as Syed Farook, US media reported.
"We have a domestic terrorist-type situation here. The suspects were armed with long guns. They came prepared to do what they did, as if they were on a mission," Burguan said.
Authorities are tracing the origin of the four weapons recovered - two assault-style rifles and two handguns - from the two dead suspects, a federal law enforcement official told USA TODAY.
One police officer is among 17 people injured in the attack.
The official, who is not authorised to comment, said investigators are focusing on an incident, perhaps a workplace dispute, prior to the shooting in which one person became angry and left a gathering of employees. The person later returned with two others.
In an interview to CBS news US President Barack Obama concedes that new laws can't stop every mass shooting, but can "improve the odds that they don't happen as frequently".
"The one thing we do know is that we have a pattern now of mass shootings in this country that has no parallel anywhere else in the world," Obama said.
California Governor Edmund Brown said his administration will spare no effort in bringing these killers to justice.