Cathay Pacific Airways is investigating how multiple oxygen bottles were emptied on board two of its aircraft while on the ground in Toronto.

The incident comes at a sensitive time for the airline, as Chinese authorities have asked for assurances of the carrier’s safety and security procedures in the wake of widespread

civil unrest in the airline’s headquarters city of Hong Kong. There is no indication yet as to how the bottles were discharged.

On Aug. 27, Cathay confirmed that several portable oxygen bottles on board two aircraft “were found to be discharged or partially discharged.” Five bottles on one aircraft and eight on the other were affected, out of 22 on each aircraft.

Cathay stressed that it “identified the issue prior to departure during its routine inspections that it carries out before every flight.” The airline said the emptied bottles “were immediately recharged and checked for serviceability by engineers prior to their flights.” The portable bottles are for the use of cabin crew members so they can move around an aircraft during emergencies.

“At no point was the safety of our crew and passengers compromised,” Cathay said. However, the carrier said it is “taking the issue very seriously and has launched an internal investigation into the matter.”

The Civil Aviation Administration of China (CAAC) recently issued a new set of requirements to Cathay in response to the Hong Kong protests. According to the airline, one of the requirements was to submit a report “providing details of actions taken to step up internal safety controls and improve flight safety and security.”

The CAAC also stipulated that no Cathay employees involved in “illegal protests, violent actions or overly radical behavior” would be allowed on flights entering Chinese airspace, and the airline must submit crew lists on such flights for approval.

Cathay has said it will comply fully with the CAAC directives and have zero tolerance for workers involved in illegal activities, including illegal protests.

At least four Cathay workers—including two pilots—have been dismissed for actions related to the protests. Some of the workers had misused airline passenger data.

Adrian Schofield,