The missile was launched from the Wonsan area at around 6.30am on Saturday and flew more than 700km, the South Korean military said in a statement. Seoul and Washington were analysing the test for details.
Japan's coast guard, in a statement citing the Japanese defence ministry, said the object may have been a ballistic missile and appeared to have come down, warning ships to take precautions.
South Korea's military said it has raised its monitoring of any further missile tests and will share intelligence with the United States and Japan.
The South Korean presidential office's national security council convened an emergency meeting on Saturday to assess the situation after the missile launch, the office said in a statement.
North Korea has launched missile tests on more than 10 occasions so far in 2026. Pyongyang has sometimes said it was testing new types of weapons systems. Some of the tests have come after North Korea protested joint military drills between Seoul and Washington.
The launch came after Pyongyang's Kim Yo -jong, the powerful sister of leader Kim Jong-un, issued a statement on Friday that dismissed Seoul's demand for an apology for what it said were North Korean mines that seriously wounded South Korean soldiers in the Demilitarised Zone, a heavily fortified area between the two Koreas.
South Korea this week said North Korean mines caused the blast that seriously injured two South Korean soldiers on a reconnaissance mission inside the four-kilometre-wide border that stretches across the Korean Peninsula.
The missile test may be an attempt by Pyongyang to draw a response from South Korea to the sister's statement, said Cheong Seong-chang, vice president at the Sejong Institute in Seoul, a research centre on North Korean affairs. North Korea may also have tested a new type of missile, he said.
North Korea has sharply ramped up hostility against the South in recent years, disavowing unification as a national goal and calling South Korea its "primary foe".
