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".
In a statement to the BBC, Singapore Airlines said it made the change after Pyongyang launched an intercontinental ballistic missile (ICBM) in July. The French airline expanded its no-fly zone over North Korea as a result.
Airlines operating routes between Korea and the United States are changing flight paths to avoid areas that may be exposed to missile launches from North Korea.
Singapore's flag carrier has changed its Seoul to Los Angeles route as a precautionary step against missile launches from North Korea.
The Hong Kong based airline sent out a staff note earlier this week sharing the communications from the cockpit, with the crew saying "we witnessed the DPRK missile blow up and fall apart near our current location".
According to guidelines issued by the International Civil Aviation Organisation (ICAO), a UN agency in charge of air safety, nations have the "responsibility to issue risk advisories regarding any threats to the safety of civilian aircraft operating in their airspace". However, it has failed to give prior notice before its various missile tests this year.
The South China Morning Post says radar information shows other airlines were also flying in the general area of the test-including two Taiwanese airlines flying to Taipei from Vancouver and Seattle....and a Japanese airline flying from Frankfurt to Tokyo.
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.