A gunman with a semi-automatic weapon shot three people, killing a federal security agent, at the Los Angeles airport Friday, officials said, and a suspect was in custody. Flights were disrupted nationwide.

Los Angeles police Assistant Chief Earl Paysinger said the unidentified suspect apparently was injured following an exchange of gunfire with officers.

Officials told a press conference they saw no further threat Friday to the nation's third largest airport, which is a major gateway for flights to Asia, Australia and New Zealand.

Los Angeles Airport Police Chief Patrick Gannon said the gunman entered the terminal, pulled an assault rifle from a bag and began shooting at a screening checkpoint before entering the terminal. He said the lone shooter approached a security agent who was checking passenger documents and opened fire.

"As you can imagine, a large amount of chaos took place in this entire incident," Gannon said. Officers took the gunman into custody after a shootout.

Some passengers were evacuated, while others were locked down in airport restaurants and lounges. The airport was being swept as part of precautionary measures, and the bomb unit was on the scene.

Tim Kauffman, a spokesman for the American Federation of Government Employees in Washington, confirmed that a Transportation Security Administration officer was killed. He said the union's information came from their local officials in Los Angeles.

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."

Interim Los Angeles Fire Chief Jim Featherstone said paramedics treated seven people at the scene, and six were taken to hospitals.

The gunshots were reported at Terminal 3, which is home to Virgin America and other airlines.

Air traffic was affected nationwide as the Federal Aviation Administration 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.

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," Rosen said.

Airport security staff evacuated terminals, including onto to the tarmac. Hundreds of people remained gathered outside next to airplanes.

LAX air traffic controller Michael 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."

Flight tracking site FlightAware.com said that as of 11 a.m. local time, there were 12 flight cancelations and 132 flight delays in Los Angeles.