"South Korea and the United States are aware of the North Korean missile launch," said a spokesman for Seoul's defence ministry, adding they "suspect it was a failure".
The ministry did not identify the type of missile used in the test.
Japanese Kyodo news service, citing an unidentified government source, said the North might have launched several missiles Wednesday morning.
The missiles were possibly launched from North Korea's east, Kyodo's source said, adding that there was information that the launches were a failure.
Nuclear-armed North Korea launched four ballistic missiles earlier this month, with three landing provocatively close to America's ally Japan.
The launches come as Seoul and Washington hold large-scale annual joint military exercises that always infuriate Pyongyang, which sees them as a rehearsal for invasion.
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