UPDATE 12.40am: Police have confirmed two suspects -- one male, one female -- were killed in the SUV chase. One further man, possibly a suspect but not confirmed, is in police custody.
Both killed suspects were reportedly dressed in tactical-style clothing and armed with assault rifles. An FBI spokesperson said it was "a possiblity" that the incident was related to terrorism, but the agency was "still not sure."
Police say they identified a possible explosive device inside the Inland Regional Center, but are still searching the facility.
A tip after the center shooting but before the car pursuit led police to a home, from where the SUV allegedly took off with the man and woman inside. A third man was seen running from the home, and was soon detained by police.
UPDATE 11.05am: Police have confirmed at least one suspect has been hit, that two "are being dealt with" and "possibly a suspect is outstanding."
A police spokeswoman said police "were doing follow-up work when they located what appeared to be the suspects [in the black SUV]. Shots were exchanged, one officer was injured and transported to a local hospital." The injured officer is not thought to be in a life-threatening condition.
Police are currently moving through the neighbourhood, seemingly searching houses and yards.
UPDATE 10.50am: A SWAT "armoured critical incident vehicle" has seemingly pulled a body out of the SUV. Police are investigating what is inside the car.
UPDATE 10.45am: Police and SWAT have surrounded the shot SUV. Reports claim a suspect is in the back of the car -- it is unclear whether alive or dead -- but allegedly has a gun strapped to his body. Other reports claim police have found a pipe bomb in or near the SUV. Bomb disposal equipment is being brought to the scene.
UPDATE 10.20am: Police have pursed and shot a fleeing SUV, similar to the one reportedly seen leaving the scene of the shooting. A body can be seen on the ground at the scene. Dozens of police vehicles responded to the scene, where occupants of the SUV allegedly shot at chasing police.
In another update to press at 10.25am, police were unable to confirm any details around the SUV shooting incident, which had occurred just minutes before. A police officer was reportedly hurt during the incident.
EARLIER: At least 28 victims have been reported in a mass shooting near Los Angeles, with police and SWAT teams dealing with a number of heavily-armed offenders and a bomb threat.
The Inland Regional Center, a social services centre in San Bernardino, about 100 kilometres south-east of Los Angeles, was the target of the shooting. The city's fire department reported the incident around 6.15am (AEDT), or 11.15am local time.
Reports from the scene suggested three gunmen were behind the attack. At a press conference at 9am AEDT (2pm local time), police said at least 14 people were dead and at least 14 had been wounded, with some injuries "significant".
Earlier reports had suggested the gunmen were holding people hostage inside the building, but police now believe the offenders fled the scene in a black SUV.
The men were said to be heavily-armed and clad in body armour, some reports claiming they were wearing camouflage gear and masks. Police chief Jarrod Burguan said the gunmen were armed with "long guns, not handguns" but could not provide any more information on their weapons.
Responding to questions about whether the incident was terrorism-related, Burguan said: "At minimum we have a domestic terrorism incident that occurred here".
He added police believed the offenders "came to do what they did, as if they were on a mission".
Pictures from the scene show a bomb investigating robot and bomb squad, and the LA Times is reporting police have detonated a suspicious device.
Reports also claim the shooting happened in a conference room rented by an outside group for a Christmas party. Burguan was unable to confirm those reports, but said the shooting seemed to be mostly confined to one area of the facility.
Witness Jose Serrano told The Huffington Post US he was at a nearby supply company when police swarmed the adjacent Inland Regional Center. He claimed he and 20 other people were hiding inside their building.
“Oh my god, there’s gotta be at least 100 cop cars,” Serrano told HuffPost.
“I’ve seen people on gurneys getting into the ambulances."
President Obama has been briefed on the situation.
The shooting is said to be at least the 352nd mass shooting in the U.S. in the 336 days of 2015.
The Inland Regional Center, according to its Facebook page, "[serves] individuals with developmental disabilities" and has 670 employees. The service only yesterday posted photos and video of its Christmas party online.
America's politicians have been quick to respond online to the incident.