On Sunday, North Korean leader Kim Jong Un reportedly inspected a "super explosive" hydrogen bomb for its intercontinental ballistic missiles.
North Korea leader Kim Jon Un speaks with scientists in a handout picture reporting to show the development of an atomic bomb.
North Korea conducted its fifth test last September.
An quake registering 6.3 was detected in the secretive state just before 7am BST on Sunday 75km (45 miles) north-northwest of Kimchaek, where previous tests have been carried out.
The natural disaster was felt in northern China in Yanji, near the North Korean border, according to local media. That would be 3:30 p.m.in Seoul and Tokyo, and 2:30 a.m. EDT.
Previous recent tremors in the region have been caused by nuclear tests.
An "explosion" measuring 6.3 magnitude was detected in North Korea Sunday after Pyongyang said it had developed an advanced hydrogen bomb that possessed "great destructive power". The photo could not be independently verified.
US officials have said actually mounting a warhead onto a missile would amount to a significant escalation, as it would create the risk that the North was preparing an attack. The administration also reported another quake in North Korea of magnitude 4.6, which it termed as a "collapse". The 5.3-magnitude natural disaster then was about as powerful as the bomb the United States dropped on Hiroshima, Japan, in 1945, that was 15,000 tons of TNT.
South Korea's military says North Korea is believed to have conducted its sixth nuclear test.
More news: USA successfully tests missile interception in HawaiiAn quake measuring 6.3 on the Richter scale was detected in North Korea after the country conducted its sixth nuclear test, a move the U.S. and its allies in the region are likely to view as a major provocation, the media reported.
USA monitors measured a 6.3-magnitude tremor near the North's main testing site site at Punggye-ri.
Intercontinental ballistic missile (ICBM) Hwasong-14 is pictured during its second test-fire in this undated picture provided by KCNA in Pyongyang on July 29, 2017.
Yet North Korea has continued to make aggressive military actions and tests, including firing a missile over Japan just earlier this week.
All the components of the "H-bomb" were "homemade" so North Korea could produce "powerful nuclear weapons as many as it wants", the state-run Korean Central News Agency quoted Kim as saying.
Seoul's weather agency said that the seismic wave was recorded at 12.36 pm.
He earlier said that North Korea would be crossing a "red line" if it weaponises a nuclear-tipped ICBM. The location of the epicenter was near the site where the North had detonated nuclear explosions in the past.
South Korea's presidential office said Pyongyang may have conducted its long awaited sixth nuclear test.
Kim said he won't give up his nuclear weapons and missile program until the US drops its "hostile" policies such as the military drills with South Korea that ended this week.
