Pyongyang's announcement was aired by the South Korean YTN and Japanese NHK broadcasters.
An estimated capacity of North Korea's possible nuclear test may have reached 50 kilotonnes, South Korean media reported on Sunday.
North Korea claimed that no radiation leakage occurred during its test of a hydrogen bomb on Sunday, media reported.
According to the Japanese NHK broadcaster, the test was carried out successfully, with no breaches of nuclear materials to the outside.
Japan supports an urgent convocation of the United Nations Security Council (UNSC) and has filed a protest to Pyongyang over its possible sixth nuclear test, Japanese Foreign Minister Taro Kono said on Sunday.
The Japanese government has condemned North Korea in the strongest terms through its embassy in Beijing and will coordinate its actions with the United States and South Korea to request the United Nations to convene an emergency Security Council meeting, Kono said as quoted by the NHK broadcaster.
SPUTNIK/MNA