LOS ANGELES (AP) — In the moments before reports of gunshots spread panic at Los Angeles International Airport, police with weapons drawn had confronted a masked man outside a terminal who was carrying a plastic sword and dressed like Zorro.

Authorities have now determined there were no gunshots. The only people at the airport with guns Sunday night were officers, but false reports of an active shooter triggered a ripple of chaos that sent frantic travelers racing to the street and onto the tarmac.

As police tried Monday to sort out the cause of the disruption, experts said the incident — the second of its kind at a major U.S. airport in two weeks — highlights one of the challenges faced by airports at a time of terrorism and frequent unsubstantiated reports.

"You can't always avoid them, and when they occur you need to respond as if it's a legitimate attack every single time," said Anthony Roman, who runs a security consulting firm in Lynbrook, New York. "There are false alarms. There are pranksters who pull fire alarms, and we evacuate right away because we're all terrified of fire."

Investigators were focusing on what prompted the first of several 911 calls from multiple terminals, airport police officer Rob Pedregon said. The initial call came from Terminal 8 around 8:45 p.m. — about five minutes after officers detained the man dressed as Zorro.

Police found no connection between the call and the man in the costume. They were investigating a report of loud noises that spurred the first call, Pedregon said.

What followed was pandemonium similar to an incident two weeks ago at JFK Airport in New York when a raucous celebration of an Olympics victory may have led to noises people believed were shots. The chain reaction turned into a panic as crowds bolted.

On Sunday, active shooter reports quickly spread by social media and word-of-mouth, and passengers in five terminals fled or rushed through security checkpoints, airport police said.

"We were on the jetway, and someone starts pushing behind us," Jon Landis, a sales representative from Boston who was boarding a flight home, told The Associated Press. "One man was frantic, saying there was a shooter."

Security officers ordered some people to lie on hallway floors as police searched terminals. Others were ushered outside through security gates and into a parking lot, where several hundred people waited.

The scare shut down three terminals, closed roads and held flights in the air and on the ground, but no one was hurt. About 280 flights were delayed, at least 27 planes diverted and two flights canceled, airport spokeswoman Nancy Castles said.

Officers with rifles stormed the airport but uncovered no evidence of a gunman or shots fired.

With deadly terrorist bombings at airports in Brussels and Turkey this year, it's understandable that travelers are jittery. And LAX is no stranger to violence. A lone gunman shot and killed a Transportation Security Administration screening agent and wounded three other people in 2013.

"It doesn't take much for people to go into a panic mode and not think," said Douglas R. Laird, the former director of security for Northwest Airlines and a consultant to airports and airlines.

"You can't blame the police because they think something is happening. So you want to go in with your guns drawn, but that adds fuel to the fire."

Kenny Stavert, an opera singer from Houston, said the chaos began after he noticed the man dressed as Zorro at the baggage claim. He said he was nonthreatening and posed for pictures and hugged a woman before walking outside the terminal, where he was confronted by police.

"Once people started running, bags were slamming to the ground, people were falling down," Stavert said. "There was so much chaos you couldn't tell if people were falling down because they were shot."

He said rumors about an active shooter spread quickly as people turned to their phones for answers. Police and airport personnel hustled Stavert and others from the scene and told them to drop to the floor when they were deeper into the airport.

Isaac Yeffet, former head of security for El Al Israel Airlines who runs his own firm, Yeffet Security Consultants, said the root of the problem is weak airport security in the U.S. He cited a 2015 inspector general report from the Homeland Security Department that found in 67 out of 70 tests across the nation, TSA screeners failed to find mock weapons and explosives.

"When you don't have security, don't be surprised that somebody can drive you crazy with a false alarm," Yeffet said.

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Associated Press writers David Koenig in Dallas, Justin Pritchard in Los Angeles and Alina Hartounian in Phoenix contributed to this report.