North Korea fired an unidentified type of ballistic missile towards the sea off the country's east coast, Japan's Coast Guard and the South Korean military have said.
"The North fires unidentified ballistic missile(s) towards East Sea," the South Korean joint chiefs of staff. said in a statement.
No further details were immediately reported.
The launch came after warnings from officials in Seoul and Tokyo that nuclear-armed North Korea was preparing to test-fire a missile, including one of its longest-range intercontinental ballistic missiles (ICBM) this month.
All of North Korea's ballistic missile activities are banned by United Nations Security Council resolutions, though Pyongyang defends them as its sovereign right to self-defence.
The test comes as Seoul and Washington warned Pyongyang that any nuclear attack on the United States and South Korea would result in the end of the North Korean regime.
The two allies held their second session of the Nuclear Consultative Group in Washington on Friday, where they discussed nuclear deterrence in the event of conflict with the North.
The launch also comes as Pyongyang marks the anniversary of the death of leader Kim Jong Un's father and predecessor Kim Jong Il who died on December 17, 2011.
North Korea last year declared itself an "irreversible" nuclear power and has repeatedly said it will never give up its nuclear programme, which the regime views as essential for its survival.
And last month Pyongyang successfully put a military spy satellite into orbit. It has since claimed its eye in the sky was already providing images of major US and South Korean military sites.
