Passengers ran through security without being screened at Las Vegas airport after hearing a loud noise.
This caused delays and cancellations on Sunday as concourses had to be cleared and passengers re-screened.
Police said reports of a shooting were "unfounded," blaming the noise on an "unruly subject."
Passengers ran through security without being screened at Las Vegas' Harry Reid International Airport on Sunday morning after hearing a "loud noise," causing chaos including flight delays.
Social media posts suggested that panic began when passengers and staff heard what they thought was a gunshot. Las Vegas police said that reports of a shooting in terminal one of the airport were "unfounded."
"The noise is believed to have been caused by an unruly subject," the police department said in a statement posted to Twitter.
"That person is currently in custody," it added. The person's status as of Monday morning is unknown.
The noise "caused a panic among travelers, subsequently creating a security incident when some people rushed through security checkpoints," the airport said.
"As a result, passengers from multiple concourses needed to return to checkpoints to be re-screened before boarding aircraft."
One person shared a video to Twitter of people shouting and running through security, including what appeared to be staff in Transportation Security Administration uniforms.
In another video, a passenger at the airport said: "No one knows what's happening ... Everyone's just running, we have no idea why."
The passenger, who was only wearing one shoe, said that people had pushed down the gates at security.
Another passenger said that he heard someone scream "gun" and hid in a stairwell with other passengers until they got the all-clear from security.
"People rushed the TSA checkpoint knocking things over and trampling other folks," he tweeted. "I've heard of injuries like a broken foot."
Soon after the incident, the airport said that delays would likely continue throughout Sunday as concourses were cleared and passengers were screened.
It also warned that cancellations were possible. Photos and videos posted on social media showed huge lines at the airport, including one line so long that people had to queue outside the terminal building.
Around 30% of flights to and from the airport were delayed on Sunday while 32 flights, or around 3%, were canceled, according to data from flight-tracking site FlightAware.
The incident at Las Vegas Airport comes amid a summer already beset by travel chaos.
Passenger numbers are almost back to prepandemic levels, but airports and airlines don't have as many workers because of layoffs, strikes, and resignations. This has led to flight delays, cancellations, long lines at security, and lost luggage.
Almost 4.7 million passengers traveled through Las Vegas Airport in June, which the airport said was its "busiest month ever."