Air Canada says it is investigating after passengers arriving at Vancouver International Airport from Beijing were able to enter the country without being screened by customs.

The airline says a number of passengers on board Air Canada Flight 030, which landed in Vancouver around 11:30 a.m. PT Sunday, were "misdirected into the Domestic Terminal" instead of customs and immigration.

Richmond RCMP and the Vancouver Airport Authority were called in to corral the more than 200 customers who were still at the airport.

"As soon as this inadvertent error was noticed, passengers disembarking were then directed directly to Canada Customs as per the normal process," said Air Canada spokeswoman Angela Mah in an email.

"The vast majority of passengers initially misdirected were subsequently located and they subsequently cleared Canada Customs."

People missed connections

WestJet flight attendant Crystal Friesen told CBC News she was a passenger on Air Canada Flight 030 and alerted airport officials to the customs breach.

WestJet flight attendant Crystal Friesen says she was on the Air Canada Flight 030 from Beijing to Vancouver on Sunday when passengers were allowed off the plane and into the domestic baggage claim without going through Canada Customs.

Friesen said everyone walked off the plane and down to the domestic baggage claim. When the luggage didn't arrive, she said, she knew something was wrong. She went back upstairs and told a customer service agent what was happening.

"He said, 'Oh that's the first I've heard about it.' So then he went and talked to another lady about it. She came out. They didn't really know what to do."

Friesen said the agents eventually corralled passengers and took them downstairs to be properly screened by Canada Customs. She said it took about an hour and a half just to clear the first 40 passengers in line.

"Some people were upset. There were a lot of Chinese, and I don't think they understood what was going on. A lot of people had connecting flights that they were now missing."

Air Canada investigates

Friesen figured the breach happened because a customer service agent failed to properly bridge the aircraft.

"If it's a domestic arrival, they open one gate and you're released into domestic arrivals. But what they did was they didn't close that gate and they didn't open the international arrival gate," she said.

"If I hadn't had luggage, I would have just left.… Anybody who had carry-on only, they probably would have just walked right out the door."

​Air Canada said it has launched an internal investigation into the customs breach, and is working closely with the airport authority and Canada Border Services Agency.

Andre Gerolymatos, a Simon Fraser University professor who specializes in international security and terrorism, says Air Canada could still face a fine even if it was a mistake.

"Mistakes happen. We're human," he said, but added that "it's very important the company that runs security takes the responsibility and let the public know what they'll do in future."

RCMP, Canada Border Services Agency, Air Canada and Vancouver International Airport wouldn't say how many people managed to exit the airport without clearing customs.

Were you or someone you know on board Air Canada Flight 030 on Sunday? If so, please contact us at cbcnewsvancouver@cbc.ca