A U.S. citizen is facing a mischief charge after trying to board a flight with a "mock improvised explosive device" at Toronto's Pearson airport this morning, in an incident that caused an hours-long delay for passengers.

United Airlines Flight 547 was set to depart at 7 a.m. ET for O'Hare International Airport, but during security clearance, U.S. Customs and Border Protection officers found a device in a passenger's suitcase that caused them concern.

According to a statement, U.S. officials notified Canadian Air Transport Security Authority officials who "swabbed the mock IED for explosives with a negative result."

While this happened, U.S. Customs officials stopped processing passengers in the airport's pre-clearance facility.

Passengers already aboard the flight were taken by bus to an isolation area, where they and their luggage were "rescreened."

Both U.S. officials and Peel Regional Police said there was no threat to passengers and that complete and "normal operations have resumed."

Man in custody

Peel police said a 58-year-old U.S. man, Joseph Galaska, has been arrested and will face a charge of mischief in connection with the security breach. He is being held in custody for a bail hearing and won't travel to Chicago when the flight departs.

Police said the date of his hearing has yet to be determined.

Anthony Bucci, a spokesperson with U.S. Customs and Border Protection, said it's unclear why the passenger tried to bring the device aboard the flight.

"I can't speak to why the person would do that," Bucci told CBC News from New York City. "When we encountered it, out of an abundance of caution, we're going to treat it like it's a real thing. And we're going to involve local partners there to ensure it's not a real IED.

"Fortunately it turned out to be a fake."

.<a href="https://twitter.com/united">@united</a> From plane to bus. Off to the isolation area we go. <a href="https://t.co/8xhuNT1zGy">pic.twitter.com/8xhuNT1zGy</a> —@jdgemm

A passenger on the flight, Joe Sturonas, said everyone on board was told there had been a major security breach and they would get periodic updates.

"There were a couple of different scenarios we were told … that dogs might be coming on board — and we were going to be taxied over to an isolation area," he told CBC News.

Another passenger, Dal Gemmell, tweeted about the situation, describing how passengers were moved from the plane into an isolation area for further screening. Gemmell tweeted that he missed his connecting flight.

United Airlines says it will offer the 169 passengers affected by the delay some form of compensation. (Paul Smith/CBC)

Just after 1:30 p.m. ET, Gemmell tweeted that passengers who didn't check in their luggage were being released from the isolation area and rebooking had begun.

According to United Airlines, the flight is expected to depart around 4 p.m. ET.

The airline said it will offer the 169 passengers who have been affected some form of compensation, but wouldn't provide details on what it would be.

Transport Canada to launch inquiry

Canada's Minister of Transport Marc Garneau said his department will be launching an inquiry.

"I think that Canadians should know that we take security at our airports extremely seriously," he said. "But we need to get to the bottom of this situation and that's what our Transport Canada inquiry is going to do."

The incident also got reaction from Public Safety Minister Ralph Goodale, who commended the Canadian Border Services Agency (CBSA).

"CBSA is always alert to events at the border that may present a risk one way or another," he said. "The [officers] are there to treat travellers in a professional, consistent, respectful way, but they're also there with a very serious mandate for safety."

4 hrs waiting on plane and 2 hrs in isolation area by yourself, tough. With small kids, really tough. #547 <a href="https://t.co/yNzYnY5uo2">pic.twitter.com/yNzYnY5uo2</a> —@jdgemm