It means this latest device was about five times larger than the bomb dropped on the Japanese city of Nagasaki in World War II.
China has expressed annoyance at North Korea's frequent ballistic missile launches, but analysts have said China probably would not take serious action - unless there is another nuclear test.
The reports come just as South Korean media claims that a 6.3 magnitude quake in North Korea may be due to the country having performed its sixth nuclear test.
KRT did not give any details of the announcement, but it comes after quake activity was detected earlier Sunday in what is presumed to have been a North Korean nuclear test.
The first ever ICBM test was conducted last July.More news: Area gas prices up 14 cents in recent days
Experts and officials have said North Korea could conduct its sixth nuclear test at any time, and that the reclusive country has maintained a readiness at its nuclear test site to conduct another detonation test.
It's understood Japan's Ministry of Defence dispatched at least three military jets to test radiation levels.
Another threat is deemed to be looming ahead as North Korean leader Kim Jong Un has been spotted inspecting a new, ultra explosive hydrogen bomb.
The state-owned broadcaster is the only official source of television news for North Koreans.
North Korea conducted two nuclear tests last year, the last almost a year ago, on the September 9 anniversary of the nation's founding.
The blast first measured in at 5.6 on the Richter scale but has since been revised up to a much stronger 6.3.
It isn't immediately clear whether North Korea has conducted its sixth nuclear test.More news: Windows Fall Creators Update available from October 17th
"South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!"
Following the reports of the seismic activity in the North, Moon immediately convened a meeting of his national security council.
No further information was available at the time of writing.
Earlier Sunday, Pyongyang claimed it had developed a hydrogen bomb that can be mounted on the tip of an intercontinental ballistic missile - and threatened a high-altitude nuclear explosion that experts fear could wipe out United States electrical networks.
North Korea's state-run media claimed that the country has developed the ability to load a hydrogen bomb onto a new intercontinental ballistic missile, although some outside experts already cast doubts on the claim.
Even more troubling is that Kim is threatening the capability of a catastrophic EMP attack that could be directed at the U.S.
In what could be read as a veiled warning of more nuclear tests, Kim underlined the need for scientists to "dynamically conduct the campaign for successfully concluding the final-stage research and development for perfecting the state nuclear force" and "set forth tasks to be fulfilled in the research into nukes".More news: Amber Alert for mom, 1 year old canceled