LOS ANGELES (AP) — A gunman armed with a semi-automatic rifle opened fire at Los Angeles International Airport on Friday, killing a Transportation Security Administration employee and wounding two other people in an attack that frightened passengers and disrupted flights nationwide.

Police said the unidentified suspect, who was apparently injured following an exchange of gunfire with officers, was in custody.

Tim Kauffman, a spokesman for the American Federation of Government Employees in Washington, confirmed Friday that a TSA officer was killed. Kauffman said the union's information comes from their local officials in Los Angeles.

Los Angeles Airport Police Chief Patrick Gannon said the gunman pulled what he described as an "assault rifle" from a bag and began firing. "As you can imagine, a large amount of chaos took place in this entire incident," he said.

Some passengers who already had cleared security rushed onto the tarmac to evacuate, while others were locked down in airport restaurants and lounges. The airport was being swept for precautionary measures and the bomb unit was on scene.

Air traffic was affected nationwide as the FAA grounded flights that had not yet departed for LAX.

Witness Brian Keech said he heard "about a dozen gunshots" from inside a security gate at the terminal, which has been evacuated.

Ben Rosen was sitting at the Starbucks in Terminal 3 eating oatmeal at about 9:20 a.m. when he heard gunfire erupt and people start running in all directions and others crouching on the ground. Rosen got on the ground and another passenger said "don't worry we're safe."

Then more gunshots erupted. He grabbed his phone and tried to lie down as flat on the ground as he could. Police showed up with their guns drawn, shouting, "This is not a drill, hands up."

Everyone put their hands up and then were led out of the airport terminal to the international terminal, Rosen said.

As they were led out they saw broken glass from a window that looked like it'd been shot out. Rosen left his bag behind.

"It was scary I've never experienced anything like this before," he said.

The Federal Aviation Administration said a "ground stop" was in affect for all flights heading to Los Angeles, meaning planes in any other airport in the country can't take off for the city, although some flights already in the air were allowed to land.

LAX air traffic controller Michael Foote said some flights were still being allowed to depart.

Foote said his colleagues in the control tower saw passengers spilling from the terminal onto the tarmac, "evacuating the building, getting out as fast as they could." Officers eventually corralled them.

Other travelers described a chaotic scene as airport security staff evacuated terminals, including onto to the tarmac. Hundreds of people remained gathered outside next to airplanes as authorities investigated what happened.

"People started saying there's a shooter, there's a shooter," said Natalie Morin, a senior at USC who was heading to San Francisco for a graduate school interview.

Emergency crews responded to a multi-patient incident, Fire Department spokesman Brian Humphrey said. Terminal 3 is home to Virgin America and other airlines.