LOS ANGELES — A gunman armed with a semi-automatic rifle opened fire at the Los Angeles International Airport on Friday, wounding a Transportation Security Administration employee and two others 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.

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.

LAPD Assistant Chief Earl Paysinger said the TSA employee was injured and transported to the hospital after the shooting in Terminal 3.

Ronald Reagan UCLA Medical Center said it received “three male victims from the LAX Airport shootings. One arrived in critical condition and two are listed in fair condition.”

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

Witness Brian Keech told The Associated Press he heard “about a dozen gunshots” from inside a security gate at the terminal, which has been evacuated.

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.