North Korea fired a ballistic missile towards the sea off its east coast on Sunday, ahead of planned military drills by South Korean and US forces involving an aircraft carrier and a visit to the region by US Vice President Kamala Harris, Reuters reported.
Japan's public broadcaster NHK also said the object appeared to have fallen outside the country's exclusive economic zone.
Hours later, South Korea said the North had launched one short-range ballistic missile from near its capital city, Pyongyang.
Japan Defense Minister Yasukazu Hamada said the North Korean missile reached an altitude of 50 kilometers and it may have flown on an irregular trajectory.
"If you include launches of cruise missiles this is the nineteenth launch, which is an unprecedented pace," he added.
South Korea's military, however, said it was a single, short-range ballistic missile fired from near the Taechon area of North Pyongyang Province just before 7 a.m. local time and flew about 600 km (373 miles) at an altitude of 60 km and a speed of Mach 5.