Atlanta, Georgia (CNN) -- Canadian authorities are investigating an "unbelievable" incident in which a passenger boarded an Air Canada flight disguised as an elderly man, according to a confidential alert obtained by CNN.

The incident occurred on October 29 on Air Canada flight AC018 to Vancouver originating in Hong Kong. An intelligence alert from the Canada Border Services Agency describes the incident as an "unbelievable case of concealment."

"Information was received from Air Canada Corporate Security regarding a possible imposter on a flight originating from Hong Kong," the alert says. "The passenger in question was observed at the beginning of the flight to be an elderly Caucasian male who appeared to have young looking hands. During the flight the subject attended the washroom and emerged an Asian looking male that appeared to be in his early 20s."

After landing in Canada, Border Services Officers (BSOs) escorted the man off the plane where he "proceeded to make a claim for refugee protection," the alert says.

"The subject initially claimed to be in possession of one bag; however, flight crew approached the BSOs with two additional pieces of luggage which were believed to belong to the subject. One bag contained the subject's personal clothing items while the second contained a pair of gloves. The third contained a 'disguise kit' which consisted of a silicone type head and neck mask of an elderly Caucasian male, a brown leather cap, glasses and a thin brown cardigan."

The man put on the disguise for the officers who "noted he very much resembled an elderly Caucasian man, complete with mimicking the movements of an elderly person. The subject admitted at this time that he had boarded the flight with the mask on and had removed it several hours later," according to the alert.

Read the intelligence alert

"We can confirm that officials from the CBSA met a passenger arriving off AC018 Hong Kong to Vancouver on October 29 and the matter is still under investigation," said Air Canada spokesman Peter Fitzpatrick, who noted that "there are multiple identity checks before departure at the Hong Kong international airport, including Chinese government-run Hong Kong passport control, which Hong Kong originating passengers must undergo."

Hong Kong officials said they are aware of the incident and would call back with more information later.

Jennifer Bourque, regional communications officer for the CBSA, confirmed that "we intercepted an individual, on October 29, attempting to enter Canada under false pretenses on-board an Air Canada flight."

"CBSA can confirm that the foreign national is currently in CBSA detention," she said. "The individual will present before an IRB hearing. The officials of the CBSA will not disclose further information on this file."

Because of Privacy Act regulations, she said, she cannot provide details about specific cases.

"However, I can tell you that CBSA officers examine all passengers arriving on international flights at Vancouver International Airport," she said. "CBSA works closely with air carriers and local, national and international law enforcement partners, to ensure the safety of our borders and our communities. Getting the right information at the right time is a key element in keeping Canada's border closed to safety and security threats."

The agency would not discuss when or why the man put on the disguise or details about how he boarded the plane. But the alert indicated that the suspect boarded the plane with a board pass belonging to another passenger.

"It is believed that the subject and the actual United States Citizen passenger (whose date of birth is 1955) performed a boarding pass swap, with the subject using an Aeroplan card as identification to board the flight," the alert said.

Aeroplan is a credit card where card holders can earn frequent flyer miles.