Local police have confirmed the identities of two shooters involved in a mass killing in California, while a third suspect remains in custody.

A 28-year-old American resident, Syed Rizwan Farook, and 27-year-old Tashfeen Malik were killed in a police shootout in San Bernardino following the deadliest gun violence incident the country has seen since the Sandy Hook massacre in 2012.

Fourteen people were confirmed dead and another 17 injured when the shooters opened fire during a Christmas holiday event at the Inland Regional Center in the southern Californian town of San Bernardino. A third unidentified person was in police custody on Thursday afternoon (AEDT), but it remained unclear if they were involved.

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Farook had worked for the San Bernardino County as an environmental health specialist for the past five years and was present at a function at the Center before the shooting.

San Bernardino Police Chief Jarrod Burguan said there was little known about Malik and they had been unable to confirm if the pair were “husband and wife [or] boyfriend and girlfriend”.

Farook left the venue “under some circumstances that were described as angry”, but a motive was not known. They have not ruled out terrorism.

Farook’s brother-in-law, Farhan Khan, who is married to Farook’s sister, spoke at a media conference held by the Council on American-Islamic Relations (CAIR) earlier on Thursday.

“I cannot express how sad I am for what happened today,” he said.

“I am in shock that something like this could happen.”

Law enforcement officers investigate a suspicious bag, later found not to be a threat, on Victoria Avenue. Photo: AAP

CAIR also condemned the “horrific and revolting attack”.

San Bernardino Mayor Carey Davis described the shooting as a “shocking event for our community”.

“There has been a great outpouring of support and assistance to our community,” Mayor Davis said.

“We as a city will do all we can for the victims of this violent crime.

“As a city we are still on alert, the police department is in full force and bringing in all the resources they can.”

Police caught the suspects after a dramatic chase and stand-off led to one officer being wounded and taken to hospital with non-life threatening injuries. They remained in hospital that night.

The officer was said to have stopped a black SUV carrying the suspects.

The FBI searched a home in the nearby suburb of Redlands, in connection with the shooting.

Several reporters at the scene said they saw a robot device going into the home ahead of police, and a loud noise was heard a short time later.

It was unclear if anyone was inside the home at the time of the search.

Brother-in-law of Syed Farook says he is “in shock something like this could happen” after #SanBernardino shooting. https://t.co/BEFqnNP2c6

— CNN Tonight (@CNNTonight) December 3, 2015

Mr Burguan said the home was one property listed as an address of the pair, but they had not confirmed if they were living there.

A third suspect was “seen running away” but was eventually detained by authorities.

The suspects reportedly managed to escape the scene of the shooting crime in a black SUV.

“They were dressed in assault style clothing … they were both armed with assault rifles. They were both armed with handguns,” Mr Burguan said.

After the stand-off, television pictures showed the vehicle with its windows shattered by bullets and what seemed to be a body close by.

‘Truly a tragedy in our country’

Mr Burguan has held several media conferences through the day. Photo: AAP

David Bowditch, assistant director in the FBI’s Los Angeles office, acknowledged there was a “possibility” that incident was terrorism-related and that nothing was being ruled out.

Mr Bowditch said the massacre was “truly a tragedy in our country”.

It was 12 hours after the shooting before police could begin to process the initial scene. Earlier, three devices, believed to be explosive, had been discovered. It wasn’t until they were secured that police could begin to assess the scene.

Mr Burguan said said investigators were not sure what they were made of, but that they were “leaning a little bit more toward a pipe bomb type design.”

The events of the day

The tragic incident began at 7am (AEDT) on Thursday when shooters walked into a conference room at the Inland Regional Center (a map of which is viewable below) in San Bernardino, California. 

According to police, a Christmas function was occurring in the room and there were reports of a dispute.

Farook had left the party before later returning with weapons, two handguns and two long guns, and Malik.

Two of the firearms were traced back to the suspects, according to the American authorities.

The rest of the Center houses facilities for helping people live with disabilities – and is one the biggest of its kind in the state.

Mr Burguan said he was “confident” the surrounding areas of San Bernardino were safe from assailants.

“We feel confident about the neighbourhood … and there is nobody outstanding there. We are reasonably confident on that,” he continued.

A woman wipes tears near where families are gathering to pick up loved ones from the centre. Photo: AAP

“We will continue to identify if there was a third person involved or more people that might have been involved in the planning. We are early on that part of the investigation.”

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US President Barack Obama offered his condolences and said the “pattern” of mass shootings in the country had to be rectified.

“We have a pattern now of mass shooting in this country that has no parallel anywhere else in the world.” he said.

California Governor Edmund G. Brown Jr. added: “Our thoughts and prayers are with the victims’ families and everyone affected by the brutal attack.

“California will spare no effort in bringing these killers to justice.”

A man, whose wife was in the building at the time of the shooting, told ABC7 that people in the centre “saw bodies on the floor”.

“She [my wife] said the guy came in next to her office and started shooting so she locked herself in the office and they saw bodies on the floor.”

Just over 200,000 people live in San Bernardino, which is located in southern California. The city is about 95km east of Los Angeles.