In an "unprecedented, grave and serious" threat, nuclear-armed North Korea test-fired a ballistic missile over Hokkaido on Tuesday morning, the first unannounced launch of a missile to fly over Japan.

The Japanese government said the missile flew over southern Hokkaido for two minutes, later breaking into three segments before plunging into the Pacific Ocean about 1,180 km east of Cape Erimo.

The North launched the apparent intermediate-range missile that traveled for about 14 minutes, at 5:58 a.m., the government said, adding that no damage had been reported to ships or aircraft.