North Korea has staged a "successful" underground nuclear test, the communist state's official media has said.
Countries across the region went into crisis mode as North Korea defied international sanctions and condemnation and exploded its second nuclear device.
The underground blast took place at 0100 GMT and was said to be more powerful than their first test device which was detonated in October 2006.
South Korea National Security Council is going into emergency session.
Japan has mobilised a crisis task forces and has pledged to respond in a "responsible fashion."
China's foreign ministry says it is aware of the blast but has yet to issue a statement.
China is one of North Korea's few allies but was resolutely opposed to the nuclear test in 2006.
Confirmation of the test came from the North Korean News Agency.
"North Korea conducted one more underground nuclear test as part of measures to bolster up its nuclear deterrent for self-defence in every way.
The test will push the rogue state into further world isolation but will give Kim Jong Il a much needed boost at home. ...
BreakingNews
1. URGENT — North Korea appears to have test-fired short-range missiles after it conducted a second nuclear test, Yonhap reports.8 minutes ago from BNO Headquarters
2. BULLETIN — NORTH KOREA FIRES SHORT-RANGE MISSILES10 minutes ago from BNO Headquarters