The Korean Meteorological Administration (KMA) said that a moderate 2.1-magnitude earth tremor was in fact "artificial" seismic activity, presumed to be the result of an explosion inside a mine in the mining town of Pyonggang.
"The epicentre is measured to be near the land surface," a KMA official said.
The reports came after new activity was detected at a factory that produced North Korea's first intercontinental ballistic missiles (ICBMs) capable of reaching the United States.
The reports emerged just days after the second Trump-Kim summit in Hanoi, which finished abruptly without any deal or declaration due to the parties' failure to agree on the scale of North Korea’s denuclearization and US-led sanctions relief. US President Trump said on Wednesday he would be "disappointed" if the reports of new nuclear activity in North Korea are true.