The airlines confirmed that crew of the CX893 flight has reported the suspected sighting of the missile - which Pyongyang said can hit targets "everywhere in the world" - when they were mid-flight.
Singapore Airlines changed a flight route between South Korea and the USA earlier this year over fears about North Korean missile launches in the Asia-Pacific region, it has emerged.
Singapore Airlines has changed some of its flight routes between Asia and the U.S.in response to North Korea's missile tests, CNNMoney reported.
Civic Party's Tam said although Cathay Pacific claimed its nearest aircraft was several hundred miles away, or more than half an hour's flight, from the explosion, the threat cannot be ruled out, especially if North Korea does not announce its missile launches.
The missile was far from the plane, and operation was unaffected, Cathay said, adding that it had informed other carriers and relevant authorities.
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A spokesperson for The International Air Transport Association told reporters this week that North Korea has an obligation to provide advance notice of any missile tests, but not surprisingly, North Korea has never done so.
"At the moment, no one is changing any routes or operating parameters", the Hong Kong-based airline said in a statement. "We remain alert and [will] review the situation as it evolves". The flights, one from San Francisco and the other from Los Angeles, were both headed for Incheon, the main airport serving Seoul, South Korea.
Crew and pilots from Cathay Pacific and Korean Air said they saw a North Korean missile during flights on November 29.
The test-launch raised tension further with South Korea and the United States, who on Monday began their largest ever joint air exercise, which the North has branded an "all-out provocation".
North Korea's new missile was reportedly a new type of nuclear-capable ICBM called the Hwasong-15. "That would still be low probability but more risky".