Passengers on a flight to Chicago got a big scare when a mock explosive device turned up in a suitcase at a Toronto airport Thursday, investigators said.

Crews found the fake improvised explosive device (IED) during a pre-clearance inspection at Pearson International Airport, U.S. Customs and Border Protection said in a statement. The finding delayed the passengers' travel for hours.

The device appeared in the suitcase of a U.S. traveler on United Airlines Flight 547 headed to Chicago O'Hare International Airport. The flight was scheduled to leave 7 a.m. ET Thursday, according to the airline's website.

Police issued an alert about a "possible security breach" on Twitter as airport security swooped in to examine the device for possible explosive material. The device tested negative.

.@CustomsBorder @TorontoPearson .Re: breach investigation at Pearson Airport, the flight has been cleared there is no threat, investigation is ongoing by Peel Police. — Peel Regional Police (@PeelPoliceMedia) April 6, 2017

All the passengers and luggage on the Chicago-bound flight were taken off the flight as police searched their belongings and the plane for other possible explosives.

"For the safety of travelers within the Preclearance Facility (PCF), CBP stopped all traveler processing while the mock IED was tested," U.S. Customs and Border Protection said.

One traveler tweeted he had waited four hours just to exit the plane to go into an "isolation room."

.@united After 4 hrs waiting on flight getting ready to deplane in the rear to bus to take us to isolation area. pic.twitter.com/XmQHyqOsvN — Dal Gemmell (@jdgemm) April 6, 2017

The unidentified American man, 58, was arrested and charged with mischief, The Star reported. He is scheduled to appear in court in Brampton, Ontario, on Friday.