North Korea has launched two ballistic missiles eastward, and both of them appeared to have fallen outside Japan's exclusive economic zone, Japanese Defence Minister Yasukazu Hamada said.
The first missile reached an altitude of 50 km and covered a range of 550 km, while the second one rose as high as 50 km and flew 600 km, Hamada told reporters on Wednesday.
Japan lodged a protest against the missile launches through diplomatic channels, he said.
The launch comes less than a week after leader Kim Jong-un personally oversaw the firing of the country's newest intercontinental ballistic missile, the solid-fuel Hwasong-18, a launch Pyongyang said was a warning to the United States and other adversaries.
It is the latest in a series of weapons tests by Pyongyang and comes as Seoul and Washington ramp up defence cooperation in the face of soaring tensions with the North.
It also came a day after a US nuclear-armed ballistic missile submarine visited South Korea for the first time since the 1980s.
The move had been expected to trigger a strong response from North Korea, which baulks at having US nuclear assets deployed around the Korean peninsula.
Also on Tuesday, a US soldier facing disciplinary action fled across the inter-Korean border into North Korea.
The soldier is believed to be in North Korean custody, Washington said, creating a fresh crisis between the two foes.