North Korean leader Kim Jong-un meets top security officials in Pyongyang
North Korea says it has successfully carried out its third underground nuclear test, in a widely-anticipated move set to draw international condemnation.
Pyongyang said the test involved a "miniaturised" device and was carried out in a "perfect manner".
The confirmation came three hours after seismic activity was detected at North Korea's nuclear test site.
The UN had warned of "significant consequences" if Pyongyang went ahead, reports the BBC.
UN Secretary General Ban Ki-moon has condemned the test as a "clear and grave violation" of UN resolutions and a "deeply destabilising" provocation.
The Security Council is to hold an emergency meeting at 14:00 GMT on Tuesday in New York, diplomats say.
North Korea previously conducted nuclear tests in 2006 and 2009. It announced in January that it would conduct a third as a response to UN sanctions expanded after its December rocket launch.
Confirmation of the test came in a statement from state-run KCNA news agency.
"It was confirmed that the nuclear test that was carried out at a high level in a safe and perfect manner using a miniaturised and lighter nuclear device with greater explosive force than previously did not pose any negative impact on the surrounding ecological environment," KCNA said.
The reference to "miniaturised" is likely to alarm observers. The US and North Korea's neighbours fear Pyongyang's ultimate goal is to produce a device small enough to fit on a long-range missile.
In December it put a satellite into space using a three-stage rocket - a move condemned by the UN as a banned test of missile technology.
Monitoring agencies from several nations had detected seismic activity at the Punggye-ri underground nuclear test site at 11:57 (02:57 GMT).
A shallow earthquake with a magnitude of 4.9 was recorded, the US Geological Survey said.
Both South Korea and Japan convened emergency meetings of their national security teams shortly afterwards.
"This is an unacceptable threat to the security of the Korean peninsula and northeast Asia and a challenge to the whole international community," South Korea's presidential national security adviser Chun Young-woo said.