Police are searching for up to three gunmen who killed at least 14 people at a social services centre in San Bernardino, California.
Officers said there were also 17 wounded in the attack at the Inland Regional Center, which helps adults with disabilities.
The gunmen, in military-style clothing, entered the building and opened fire before fleeing in a black SUV.
Witnesses said people locked themselves in offices as the gunfire rang out.
Four hours after the attack, police surrounded a dark SUV with its windows shot out on a residential street.
It is unconfirmed whether it is related to the shooting, but police said one person had been killed at that scene.
The attack took place in a conference area where the San Bernardino County Department of Public Health was holding a social event, said Maybeth Field, the centre’s president.
FBI officials said they do not yet know if it was a terrorist attack but local police said it might have been domestic terrorism.
“I think what they are getting at there, following the Paris attacks, is that they do not have any direct suggestion at this stage that this is an Islamist-style terrorist attack, rather, if it is a terrorist attack it is perhaps some kind if home-grown terrorist attack here in the US,” said the BBC’s James Cook reporting from the scene.
He said that buildings surrounding where the incident occurred are closed and people are barricaded inside, and busses of people are being driven away from the scene.
One man received a text from his daughter that said she was hiding inside the building, where she works.
Terry Petit told reporters his daughter wrote to him: “People shot. In the office waiting for cops. Pray for us. I am locked in an office.”
President Barack Obama has responded to the shooting.
“One thing we do know is that we have a pattern of mass shootings in this country that has no parallel anywhere in the world,” he said.
“There are some steps that we could take, not to eliminate all incidents, but to make sure they happen less frequently.”
People were seen being led out of the Inland Regional Center, which is a health care centre that specialises in helping adults with disabilities like autism and mental health problems.
Some were wheeled away on stretchers with medics and police officers in attendance.
Marcos Aguilera’s wife was in the building when it happened. He said a gunman entered the building next to his wife’s office.
“They locked themselves in her office. They saw bodies on the floor,” he told a local ABC News station.
His wife escaped unharmed.
The shooting happened less than a week after a shooting at a Planned Parenthood clinic in Colorado left three people dead and nine people wounded. –BBC.
