The FBI says it would be premature to comment on a motivation at this time and joint investigators have neither ruled out terrorism, nor ruled it in.
A gunman opened fire with an assault rifle at Los Angeles International Airport (LAX) Friday, killing a security agent, creating scenes of chaos and causing widespread flight disruptions.
Panicked travellers scrambled to escape after the shooter, named as 23-year-old Paul Anthony Ciancia, pulled out the gun and shot his way through a security checkpoint before being stopped in an exchange of fire with police.
The victim was the first employee of the Transportation Security Administration (TSA) to be killed in the line of duty since the TSA was set up in the wake of the September 11, 2001 attacks.
Seven people were injured, but the lone gunman had lots more ammunition on him when he was arrested, said LA mayor Eric Garcetti.
"There were more than 100 more rounds that could have literally killed everybody in that terminal today," he said, praising airport police. "If it were not for their actions, there could have been a lot more damage," he said.
The motive for the shooting was unclear, but the Federal Bureau of Investigation said it could not rule out terrorism. The gunman was reported to be in critical condition in hospital.
Diving to the floor
The shooter opened fire shortly after 9am in a crowded terminal of LAX, the country's third-biggest air transport hub.
He "came into Terminal Three, pulled an assault rifle out of a bag and began to open fire," said LAX police chief Patrick Gannon.
"He proceeded up into the screening area… and continued shooting," he said.
TV footage showed people diving to the floor at the sound of gunfire and scrambling to escape the terminal.
Police chased the gunman to near a Burger King restaurant where they "engaged him in gunfire… and were able to successfully take him into custody."
The TSA, which employs screeners and guards at airports, confirmed one of its employees had died. "Multiple Transportation Security Officers (TSOs) were shot, one fatally," said a TSA statement emailed to AFP.
Later, the FBI named him as Ciancia, saying he was a LA resident but giving no further details.
Strong anti-government views
An NBC television report suggested Ciancia had "strong anti-government views," and may have had some link to the TSA and targeted TSA agents as his victims.
One eyewitness recounted the shooter dressed in greyish-green clothing with an assault rifle opening fire.
Brian Adamick, 43, said he saw a wounded TSA worker, with a bloodied ankle, board a shuttle bus helping passengers escape.
"It looked like it was straight out of the movies," he said.
In all some 750 flights were disrupted after the Federal Aviation Administration (FAA) issued a national ground-stop.
Nearly 50 were diverted to other airports, and the rest either held on the ground at LAX or at their originating airport, said Gina Marie Lindsey, head of Los Angeles World Airports.
Although there was no indication of other people being involved in the attack, the FBI said it could not rule out terrorism.
"It would be premature to comment on a motivation at this time and joint investigators have neither ruled out terrorism, nor ruled it in," said an FBI statement.
In Washington, President Barack Obama was kept up to date on the shooting. "Obviously, we've been monitoring it and we're concerned about it," Obama said.
This being Los Angeles, a number of celebrities were caught up in the action.
Hit TV show "Mad Men" was filming at LAX, next door in Terminal Four, a crew member tweeted, while actor James Franco posted a "selfie" picture of himself on a plane stopped on the tarmac by the incident.
"Some s** tbag shot up the place," he wrote in the first of a series of tweets, ending some five hours later with a more relieved message: "WE'RE OUT! - everyone was calm." – Sapa-AFP