San Bernardino - Up to three gunmen opened fire at a centre for the disabled in California on Wednesday, killing at least 14 people and triggering a dramatic street shoot-out as police hunted down the suspects.
The deadly incident was the latest in a series of mass shootings in the United States, a spiral of violence that has exasperated President Barack Obama, who once again urged Congress to pass tougher gun control measures.
Hours after the attack at the Inland Regional Center in San Bernardino, local police engaged in a shoot-out with what they believed to be the attackers' vehicle, a black SUV.
"Suspects are down, one officer wounded. Details still unfolding," tweeted San Bernardino police chief Jarrod Burguan.
Police were hunting for up to three gunmen following the attack, which also left 17 people injured, and Sergeant Vicki Cervantes told reporters one may still be on the loose.
"I believe there is still possibly a suspect outstanding," she said.
Cervantes said that a police officer suffered a non life-threatening injury during the shoot-out.
A body and what appeared to be a pool of blood could be seen near a bullet-riddled SUV that was surrounded by dozens of police vehicles.
Police swarmed the residential neighbourhood with officers, guns drawn, as residents were told to stay in their homes with the doors locked.
A massive manhunt was launched for the suspects after the late morning shooting at the Inland Regional Centre, which is about an hour's drive east of Los Angeles.
It was the country's deadliest shooting since December 14 2012, when a young man killed 26 people, including 20 children, at Sandy Hook elementary school in Newtown, Connecticut.
Burguan told reporters the gunmen were armed with long guns and "came prepared to do what they did, as if they were on a mission".
He said that while the motive and identities of the attackers were not yet known, "at a minimum, we have a domestic terrorist type situation that occurred here".
San Bernardino County Sheriff John McMahon said courts and local city and county buildings in the region were on lockdown, and police presence had been boosted at area schools as the manhunt unfolded.
Heavily armed SWAT teams, firefighters and ambulances swarmed the scene of the shooting, as police warned residents away.
The attack took place inside a packed auditorium at the Inland Regional Centre, a huge facility that employs several hundred people and assists people with developmental disabilities.
Brandon Hunt, who works at the centre, said a banquet for county personnel was being held at the auditorium.
Lavinia Johnson, the centre's executive director, said her staff waited inside the building after the shooting to be evacuated by police.
"It was a very traumatic event for us," she told CNN.
Officials earlier said police went through the building room by room to check reports of a suspicious package that may have been left by the gunmen.
Family members of employees at the site rushed to the area on hearing of the shooting and were seen frantically trying to get information about their loves ones
"It was an hour until I learned my daughter was OK," said Olivia Navarro, 63. "She was frightened when I spoke to her but she seemed calm."
Obama, who just last week made a plea for action on gun control after three people were killed at a family planning centrer in Colorado, voiced his anger once more.
"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," he told CBS News.
"There are some steps we could take, not to eliminate every one of these mass shootings, but to improve the odds that they don't happen as frequently."
The Democratic presidential hopeful Hillary Clinton tweeted: "I refuse to accept this as normal. We must take action to stop gun violence now."
Wednesday's shooting, which came less than a week after a gunman killed three people at a family planning centre in Colorado, was certain to further stoke the bitter debate about gun control in the United States.
In October, a gunman killed nine people at a community college in Oregon before turning the gun on himself.
According to the site Mass Shooting Tracker, there have been 351 mass shootings in the United States so far this year. A mass shooting is defined as four or more people shot in one incident.