One suspect is in police custody and all departures were delayed after a passenger made a "direct threat" to the safety of an Alaska Airlines aircraft Saturday at Seattle-Tacoma International Airport (SEA).

Alaska Airlines confirmed to Fox News Digital there was a security incident at about 1 p.m. involving Alaska Airlines Flight 2123, operated by Horizon Air from Seattle to Walla Walla, Washington. 

"During taxi to the runway, a guest made a direct threat to the safety of the aircraft to one of our flight attendants," a spokesperson said. "Our crew members followed their procedures and secured the aircraft on a runway away from the airport."

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Local and federal law enforcement were immediately notified and approached the aircraft.

FBI Seattle confirmed to Fox News Digital it responded along with the Port of Seattle Police Department.

The FAA issued a ground stop for the Seattle airport. (Reuters/Chris Helgren)

One suspect, who has not yet been identified, is in custody, according to the Port of Seattle and the airline.

The Federal Aviation Administration later issued a ground stop "due to security."

Two runways were closed after the incident, leaving just one open.

People sit in the central terminal looking out toward Alaska Airlines planes at Seattle-Tacoma International Airport June 19, 2024, in Seattle. (Kent Nishimura/Getty Images)

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Due to the threat, Alaska Airlines said at least six flights were canceled and two others were diverted.

"We are working to get all guests to their destinations safely and as quickly as possible," a spokesperson said.

The nature of the incident is unclear.

Alaska Airlines confirmed the incident took place on one of its flights in Seattle. (Stephen Brashear/Getty Images)

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There were 68 passengers and four crew members onboard, according to Alaska Airlines. 

Passengers were safely deplaned and will be returned to the terminal after a security screening, according to the Port of Seattle.

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The aircraft will be subject to security measures before continuing, Alaska Airlines said.