Thousands of Canadians had their flights cancelled or delayed on Sunday, as new security measures came into effect for anyone travelling to the U.S. by air.

As of 4:30 p.m. local time, 125 flights had been cancelled at Toronto's Pearson International airport, the country's busiest air-traffic hub.

Many other major airports across the country, including Vancouver and Montreal, each experienced dozens of disruptions. Most of the disruptions related to flights originating in or departing for the United States.

A list of all departures at the Greater Toronto Airports Authority website showed that many U.S.-bound flights out of Toronto's Pearson International Airport were delayed anywhere from one to four hours or more. Flights were cancelled to destinations such as Chicago, New York, Denver and Pittsburgh.

According to Flightview.com, a website that tracks air traffic at North American airports, the disruptions were particularly severe in Montreal, where 60 per cent of outbound flights were either delayed or cancelled. By comparison, about 20 per cent of flights were disrupted at Pearson, the website said.

In order to cope, Air Canada announced it had begun canceling flights to or from U.S. cities, "as a result of the new security measures imposed by Canadian and U.S. government authorities," the company said in a statement.

"Air Canada and Jazz are being forced to cancel select short-haul flights to the U.S. beginning today," the company said. "Customers can also expect potential delays on other domestic and international flights due to airport congestion and delayed aircraft."

According to GTAA spokesperson Trish Krale, many of the holdups are a result of passengers arriving at the airport unaware of new security guidelines, particularly the new limitation of one item of carry-on luggage.

"Clearly there's a learning curve for everyone involved and that's leading to some delays," Krale told CTV News Channel.

On Saturday, Transport Canada and the U.S. Transport Security Administration imposed new security measures on flights from Canada to the United States in the wake of an attempted bombing of an Amsterdam-to-Detroit flight on Christmas Day.

Umar Farouk Abdulmutallab, a 23-year-old Nigerian man, is charged with willful attempt to destroy an aircraft and with placing a destructive device on an aircraft in connection with Friday's incident.

The new security rules prompted the Canadian Air Transport Security Authority to warn passengers they should expect delays. The new rules include:

• Carry-on luggage is limited to one bag per person
• Passengers and their carry-on luggage will be searched a second time at the gate prior to boarding the aircraft
• Passengers will have to remain seated for the final hour of the flight

"Most of the delays are occurring -- or some of the delays are occurring -- because passengers come to the airport and they don't know (about the new rules), so then they're having to shuffle their baggage around," Krale told The Canadian Press.

In Vancouver Sunday morning, flights bound for Canadian destinations generally departed on schedule. But flights headed for U.S. cities were all delayed, according to the Vancouver International Airport's website.

The long list of cancellations across the country included a United Airlines flight from Denver to Calgary, a Delta Air flight from Montreal to Atlanta and an Air Canada flight from New York to Toronto.

Some of the many delays reported on Sunday:

• Vancouver to Honolulu on WestJet: 2 hours and 27 minutes late
• Montreal to Cincinnati on Delta Air: 2 hours and 34 minutes late
• Calgary to Houston on Continental Airlines: 1 hour and 28 minutes
• Toronto to Orlando on Westjet: 3 hours and 15 minutes

Former CSIS senior intelligence officer Michel Juneau-Katsuya told CTV News Channel that passengers can expect the delays to last for some time.

"Everybody is on the edge, and there will be some nervousness throughout the entire system," he said. "The authorities are going to deploy a lot of forces, a lot of personnel."

Eventually airport authorities will bring in expensive scanning devices to avoid the threat of passengers hiding explosives beneath their clothes and to speed up security checks, Juneau-Katsuya added.