The airline changed the route back in July after a previous North Korean missile test, according to CNN Money. It hadn't previously announced the change.
An airline spokesperson told CNNMoney on Wednesday that it had rerouted daily flights between the South Korean capital, Seoul, and Los Angeles after Pyongyang test-fired an intercontinental ballistic missile (ICBM) in July.
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 the plane's operation was unaffected, Cathay said, adding it had informed other carriers and relevant authorities.
An official at the Ministry of Land, Infrastructure and Transport said, "It appears that Singapore Airlines is flying over Busan and the east coast of Japan rather than flying through Gangwon Province and the East Sea".
"At the moment, no one is changing any routes or operating parameters".
The closest shave was on Nov 29, where crew on at least three commercial flights from Korean Air and Cathay Pacific reportedly saw the North Korean missile in the air before it blew up near their location.
The test-launch raised tension further with South Korea and the U.S., who on Monday began their largest ever joint air exercise, which the North has branded an "all-out provocation".
Travelers who are concerned should know the chances of an airplane colliding with a missile are extremely low: One safety analyst estimates that it is less than a billion to one.
"The problem is if the test goes awry in any way, and debris starts falling in.more heavily trafficked areas", he said in an email.
Katherine Lam is a breaking and trending news digital producer for Fox News.