US President Barack Obama has said steps need to be taken to reduce the number of mass shootings after 14 people were reported to have been killed when gunmen ran amok in California.
One or more gunmen opened fire at a social services centre, shooting multiple people, authorities said last night.
It was reported last night that a Christmas party had been taking place in a conference room at the centre.
Several law enforcement agencies converged on the scene in San Bernardino and were searching for the suspects. Triage units were being set up in the area.
Some people were seen being wheeled away on trolleys after gunfire erupted at the Inland Regional Centre. Others walked quickly from a building with their hands in the air and were searched by officers before being reunited with loved ones.
Police were working to secure the scene about 60 miles east of Los Angeles, Sgt Vicky Cervantes said. No arrests had been made last night.
The incident comes just a week after a shooting spree that killed three people and wounded nine at a family planning centre in Colorado.
Mr Obama said last night: "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. There are some steps that we could take, not to eliminate all incidents, but to make sure they happen less frequently."
Terry Petit said his daughter works at the centre in California, and he received a text from her saying she was hiding in the building after hearing gunshots. Petit choked back tears as he read the texts for reporters outside the centre. He said she wrote: "People shot. In the office waiting for cops. Pray for us. I am locked in an office."
At a Shell petrol station nearby, store manager Ana Fuentes said there was a flood of police activity in the area.
"There's maybe 150 cops going toward Hospitality Lane," she said, as sirens echoed in the background.
The centre says on its website that it provides social services to people with developmental disabilities. The city of San Bernardino has struggled to rebound after declaring bankruptcy in 2012. The city of about 214,000 is in the two-county inland region that was hit hard by the recession. The area where the shooting happened is along a main city road that fronts a city golf course and recreation centre.
Ms Cervantes told KCBS-TV: Tthere are multiple casualties and there are some confirmed fatalities".
She said she didn't have specific numbers.
She told the television station that it appears there was more than one shooter and they were wearing "military-style" attire.
Marcos Aguilera said his wife was inside the building when gunfire erupted but she got out unharmed.
He told KABC-TV that a shooter entered the building next to his wife's office and opened fire. He said they locked themselves in her office and saw bodies on the floor.
A local reporter tweeted that people were being evacuated from the Inland Regional Center, a medical and health organisation.
The organisation administers help to people with disabilities like autism and other mental health problems.
People were wheeled away on stretchers with medics and police officers in attendance.
CNN reported that area hospitals are receiving at least 15 patients from the shooting.
An employee of the centre told CNN that the building was holding an event for county personnel inside an auditorium when the shooting occurred.
Representatives from the FBI and the Federal Bureau of Alcohol, Tobacco and Firearms arrived on the scene.
No arrests have been made yet.
There were also unconfirmed reports of an explosive device at the scene.
Witnesses told CNN they heard rapid shooting coming from nearby the building.
Police confirmed a report that the suspects entered a conference room in the building and started shooting but had no further details.