In a statement to the BBC, Singapore Airlines said it made the change after Pyongyang launched an intercontinental ballistic missile (ICBM) in July.
Cathay Pacific said the crew of a flight from San Francisco to Hong Kong reported seeing what they thought was the missile re-entering Earth's atmosphere on November 29.
Last Wednesday, a series of ballistic missiles that the North Korea regime claimed to be able to reach the USA mainland were launched in defiance of stern warnings and global sanctions.
Korea's flag carrier Korean Air said that although it had not yet taken steps to change flight paths, it is carefully monitoring the situation, stressing that its current flight paths pose "absolutely no danger to passenger safety".
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North Korea often lobs its missiles into the East Sea. Pyongyang said the projectile flew as high as 4,475 kilometers (2,800 miles) before plummeting down into waters off the western coast of Japan.
The airline went on to state that it informed authorities and other carriers at the time. "At the moment, no one is changing any routes or operating parameters", Cathay said.
Minutes later, the pilot of another Korean Air plane reported seeing a similar flash of light, airline spokesman Cho Hyun-mook said, as cited by AP.
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Shortly after the test, a spokesperson for the U.S. Defense Department acknowledged that the North Korean missile "flew through busy airspace used by commercial airliners".
North Korea routinely fails to follow that rule and has ignored several letters from the ICAO urging it to inform airline officials of its plan to launch missiles.
Any missile launches must be reported to the International Civil Aviation Organization to assure the safety of civilian aircraft.
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.
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