In a separate message to staff, Cathay general manager Mark Hoey said the crew described seeing the missile "blow up and fall apart", the South China Morning Post reported. The missile flew ten times higher than the global space station and then back down to Earth.
The AP reported the missile was in the air for almost an hour and reached an altitude of 2,780 miles before plummeting into the Sea of Japan about 600 miles from its launch point.
Cathay said there is no current plan to change air routes, describing the flight as being "far from the event location".
The Cathay Pacific flight took off from San Francisco and was bound for Hong Kong.
The CX893 service, which was flying from San Francisco to Hong Kong from November 28 to 29 local time (HKT), was over Japan when North Korea's Hwasong-15 missile was launched, flight trackers indicated.
The International Civil Aviation Organization (ICAO) in October condemned North Korea for the repeated launching of ballistic missiles, saying they seriously threatened the safety of international civil aviation.
It also claimed the Hwasong-15 missile fired Wednesday can be tipped with a "super-large heavy warhead" capable of striking the whole United States mainland.
But analysts note the missile would require a re-entry vehicle that could withstand the heat and pressure of descent to deliver an intact nuclear warhead to the ground.
The details of the test remain unclear, with a US official saying the missile did not manage to make a re-entry into the earth atmosphere - the key problem of the rogue communist country's nuclear program.
"Coupled with the rogue regime's need to master missile guidance and targeting, the re-entry failure underscores the challenges facing the country's weapons program, according to the official".
But North Korea's tendency to launch without warning is "worrying", he added.
"It went higher, frankly, than any previous shot they've taken".
"Singapore Airlines is aware of the reports on the sighting of the North Korean missiles and is closely monitoring the situation", a spokesperson told Channel NewsAsia. Experts said it could have reached any part of continental US.
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