Air Canada and the Vancouver International Airport are investigating after a security breach Sunday afternoon allowed passengers arriving from Beijing to enter the country without going through customs.

In an email to CTV Vancouver, an airport spokesperson said a "number of passengers" from Air Canada Flight 30 were accidentally misdirected into the domestic terminal at the airport, meaning they did not have to go through customs screening first.

Passenger Crystal Friesen told CTV Vancouver that, as the passengers were leaving the airplane, the door leading towards the international terminal was closed, so all of the passengers went through the doorway leading to the domestic terminal instead.

Once she reached the baggage carousel, which is located in the public area of the terminal, Friesen realized something was wrong and she notified a staff member. Once notified, Air Canada and airport staff tried to corral the passengers and re-direct them to the international customs area, Friesen said.

The airline could not say how many passengers skipped customs screening.

"As soon as this inadvertent error was noticed, passengers disembarking were then directed directly to Canada Customs per the normal process," Air Canada spokesperson Angela Mah said, adding that the "vast majority" of passengers went through customs.

The Canada Border Services Agency said in a statement that "immediate steps" were taken to make sure the passengers underwent the necessary customs screening process.

The agency said in a statement that it is now working with airport and Air Canada staff to investigate the incident, as well as identify passengers who may have "inadvertently evaded routine process."

Richmond RCMP officers were brought in to help airport staff and CBSA officials track down passengers, but some were still able to get into the public area of the airport, Cpl. Dennis Hwang said in an email to CTV Vancouver.

"Some passengers that had not been properly screened entered the public area of the airport. Inter-agency coordination resulted in locating a majority of the unscreened passengers," Hwang said.

Airport, Air Canada, and CBSA officials all declined interview requests from CTV Vancouver.

Royston Colbourne, a security consultant with Xpera Risk Mitigation and Investigation, said it is important to determine if the breach was actually a mistake or if it was deliberate.

"One of the things we need to be confident of is that this wasn't deliberate – that it wasn't somebody working for the airport that in some ways allowed people to enter the country illegally," he said.

"Worst case scenario is that somebody or some people have entered the country that Canada would not want to enter."

Airlines can be fined for misdirecting passengers.

With a report from CTV Vancouver's Mi-Jung Lee and files from CTV Vancouver