South Korea’s Defense Ministry estimates the power of the presumed blast at 10 Kiloton,

Seismic activity has been detected in North Korea with a 5.0-magnitude earthquake at 11:58 a.m Korean time (02:58 GMT) on Tuesday. The tremor might indicate a nuclear test as earthquakes are rare in North Korea.

The quake’s epicenter was only one km deep, and was close to the North's known nuclear test site.

Yonhap quoted the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO) as saying that the seismic event in North Korea showed “clear explosion-like characteristics.”

"The event shows clear explosion-like characteristics and its location is roughly congruent with the 2006 and 2009 DPRK (North Korea) nuclear tests," CTBTO Executive Secretary Tibor Toth said in a statement.

North Korea gave the United States and China an advance notice of conducting a nuclear test the day before, Yonhap said.

The U.N. Security Council will convene for an emergency meeting at 14:00 GMT.

North Korea vowed on January 23 to strengthen its military capabilities and step up its controversial nuclear program. The announcement came as a response to the UN Security Council’s new sanctions on the country over the December rocket launch.