SEOUL — North Korea appeared to have carried out a nuclear test on Wednesday -- its fourth -- with seismologists detecting a 5.1 magnitude tremor next to its main atomic test site in the northeast of the country.
The website of the China Earthquake Network Centre described the seismic activity, which came just two days before North Korean leader Kim Jong-Un's birthday, as a "suspected explosion".
North Korea state radio said Pyongyang would make a "special announcement" at 12:00 Pyongyang time (0330 GMT). It gave no details of the content.
The US Geological Survey said the epicentre of the quake -- detected at 10:00am Pyongyang time (0130 GMT) -- was in the northeast of the country, some 50km northwest of Kilju city, placing it right next to the Punggye-ri nuclear test site.
Any confirmed test will trigger widespread international condemnation of North Korea, which has already conducted three nuclear tests in 2006, 2009 and 2013 -- all at the Punggye-ri site.
In Seoul, the presidential Blue House called an emergency meeting of the National Security Council, as officials scrambled to confirm the precise nature of the tremor.
"Further analysis is necessary to determine whether it is an artificial or a natural quake," a spokesman for the Korea Meteorological Administration said.
Researchers at the US-Korea Institute at Johns Hopkins University said last month that recent satellite images showed North Korea was excavating a new tunnel at Punggye-ri.
"While there are no indications that a nuclear test is imminent, the new tunnel adds to North Korea's ability to conduct additional detonations over the coming years if it chooses to do so," they said at the time. — AFP