North Korea has confirmed it has successfully conducted a third nuclear test, sparking alarm across north Asia.
Pyongyang says it used a miniaturized device that had a greater explosive force than previous tests.
The KCNA official news agency said the test was carried out at a high level in a safe and perfect manner.
The detonation about midday on Tuesday (local time) was caused by what South Korea calls an artificial earthquake of magnitude 5.1, sending shockwaves through the Korean peninsula.
Analysts in Seoul estimate that the yield of the blast at between 6 to 7 kilotons, or about the same or slightly larger than the North's last nuclear detonation in 2009. North Korea also conducted a test in 2006, the ABC reports.
Experts will want to establish if the rogue state used plutonium or has employed highly-enriched uranium for the first time, giving it another source of material for nuclear weapons.
The United States had warned of significant consequences if Pyongyang went ahead with a test. South Korea's defence ministry said the North gave the US and China advanced warning before conducting it.
UN to hold emergency meeting
North Korea has been threatening a nuclear test for weeks, despite warnings of severe repercussions from the United Nations Security Council.
The council is to hold an emergency meeting on Tuesday.
Diplomats have said previously that the US, South Korea and European members will want the council to adopt a resolution that would impose new sanctions on Pyongyang in the event of a third nuclear test defying earlier council resolutions, Reuters reports.
Getting approval on a resolution could, however, take weeks.