"As a ballistic missile launch like this one violates relevant UN Security Council resolutions, Japan firmly protested against North Korea and strongly condemned" the launch, Japanese government spokesman Hirokazu Matsuno said.

The reclusive state on Tuesday confirmed it planned to launch what it called a military reconnaissance satellite before June 11, having told Japan of its plans a day earlier.

Because long-range rockets and space launchers share the same technology, analysts say developing the ability to put a satellite in orbit would provide Pyongyang with cover for testing banned intercontinental ballistic missiles (ICBMs).

"We cannot tolerate this kind of launch whether it is a satellite or anything else, as it violates UN resolutions," Japan's Defence Minister Yasukazu Hamada told reporters.

Japan briefly activated its missile alert warning system for the southern Okinawa region on Wednesday morning.

But North Korean state media said the satellite had crashed into the sea soon after launch as an "accident occurred" during its flight.

Matsuno said the government presumed that the projectile "disappeared in the air above the Yellow Sea and that no object was put into outer space".

Japanese Prime Minister Fumio Kishida said earlier Wednesday that North Korea had launched "what appears to be a ballistic missile" but that there had been no reports of damage.