A man pulled a semi-automatic rifle from a bag and shot his way past a security checkpoint at Los Angeles International Airport today, killing a federal security officer and injuring two other people in an attack which disrupted flights across the US, authorities said.
The unidentified gunman was wounded in a shootout with police and taken into custody, said Los Angeles Police Assistant Chief Earl Paysinger.
The motive for the attack was not immediately clear. A Transportation Security Administration union official said a TSA officer was killed, citing local union officials.
A law enforcement official said the shooting suspect was Paul Ciancia, 23, from New Jersey. He was wearing fatigues and carrying a bag containing a handwritten note which said he "wanted to kill TSA and pigs", the official said.
Officials told a press conference they saw no further threat to the nation's third largest airport, which is a major gateway for flights to Asia, Australia and New Zealand.
The TSA issued a statement indicating that at least one other agent was injured.
Los Angeles Airport Police Chief Patrick Gannon said the gunman entered Terminal 3, pulled an assault rifle from a bag and began shooting, then fired more shots at a screening checkpoint, where a security agent was checking passenger documents, before entering the secure area of the terminal.
Officers exchanged fire with the gunman and apprehended him. Police believe he was the only person involved, Mr Gannon said.
"As you can imagine, a large amount of chaos took place in this entire incident," Mr Gannon added.
Panicked travellers dropped to the ground. Those who had passed through security fled on to the tarmac or sought cover inside restaurants and lounges.
Xavier Savant, who was waiting in the security queue where the shooting occurred, described it as a "Bam! Bam! Bam!" burst of gunfire.
Another witness, Brian Keech, said he heard "about a dozen gunshots".
Tim Kauffman, a spokesman for the American Federation of Government Employees, confirmed that a TSA officer was killed. He said the union's information came from their local officials in Los Angeles.
Six people were taken to the hospital, the Los Angeles Fire Department said. Ronald Reagan UCLA Medical Centre said it received "three male victims from the LAX Airport shootings. One arrived in critical condition and two are listed in fair condition."
Terminal 3 is home to Virgin America, AirTran, Alaska Airlines, Horizon Air, JetBlue, Virgin Australia and other airlines.
Air traffic was affected nationwide. The Federal Aviation Administration grounded flights that had not yet departed for LAX.
Ben Rosen said he heard gunfire erupt and saw people start running in all directions and others crouching. He lay on the ground. Police, with their guns drawn, shouted; "This is not a drill, hands up."
"It was scary - I've never experienced anything like this before," Mr Rosen said.
Flight tracking site FlightAware.com said that as of 11am local time, there were 12 flight cancellations and 132 flight delays in Los Angeles.