North Korea announced Wednesday it has succeeded in conducting a hydrogen bomb test, hours after what seems to be an artificial earthquake was detected close to the North's nuclear test site.

In a "special" announcement aired on the North's state television station, North Korea said it conducted an H-bomb test at 10:00 a.m. (Pyongyang Time).

"The test means a higher stage of the DPRK's development of nuclear force," the North said, referring to the acronym of the North's official name, the Democratic People's Republic of Korea.

It said in an English statement that by succeeding in the H-bomb test, North Korea "joined the advanced ranks of nuclear weapons states possessed of even H-bomb."

The announcement came as a 5.1-magnitude earthquake was detected in an area some 49 kilometers north of Kilju, home to the Punggye-ri nuclear test site on the North's northeastern tip.

The North has conducted three nuclear tests at the site, in 2006, 2009 and 2013, despite international condemnation against the tests. Pyongyang is under heavy U.N. sanctions banning its nuclear and missile tests.

Last month, North Korean leader Kim Jong-un said that the North has become a "powerful nuclear weapons state ready to detonate a self-reliant A-bomb and H-bomb."

It was the first time that Kim publicly claimed the development of a hydrogen bomb, which is much more powerful than conventional nuclear weapons.

The North's test came as a surprise as many experts said that the North's claims of hydrogen bomb development are technically unlikely for now.

North Korea did not inform China and the United States of its H-bomb test, said the National Intelligence Service, South Korea's top spy agency.

The North's leader Kim did not make any reference to its nuclear weapons program in his New Year's speech, spawning speculation that Pyongyang may seek to mend ties with China ahead of the North's party congress in May.

The Workers' Party of Korea, the North's ruling party, plans to hold its first congress in more than three decades this year.

The North's bomb test is widely expected to hurt inter-Korean ties, which have remained at a standstill following a recent breakdown in the two Koreas' recent dialogue.

South and North Korea ended their rare high-level talks on Dec.12 without any agreement over how to mend their strained relations. (Yonhap)