Japan's coast guard said the apparent missile had already fallen into the sea.
North Korea fired a ballistic missile into the Sea of Japan, also known as the East Sea, the South Korean military's Joint Chiefs of Staff said Tuesday.
The launch comes less than two weeks after Pyongyang's state media said North Korean leader Kim Jong Un had overseen a successful test of a solid-fuel engine for a "new-type intermediate-range hypersonic missile".
Japan also said it "appeared" North Korea had fired the missile, Kyodo news agency reported, adding that the country's coastguard believed the missile had fallen.
Tuesday's launch is the third ballistic missile test so far this year, after the solid-fuel one overseen by Kim in March and another tipped with a manoeuvrable hypersonic warhead in January.
The North claimed last year it had successfully tested its first solid-fuelled ICBM -- the largest, longest-range category of ballistic missile -- hailing it as a key breakthrough for the country's nuclear counterattack capabilities.
Solid-fuel missiles do not need to be fuelled before launch, making them harder to find and destroy, as well as quicker to use.
So far this year, the nuclear-armed North has declared South Korea its "principal enemy", jettisoned agencies dedicated to reunification and outreach, and threatened war over "even 0.001 mm" of territorial infringement.
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