The assessment was delivered by Nam Jae-cheol, Director of the Korea Meteorological Administration, during a hearing with members of parliament.

"Based on our analysis of satellite imagery, we judge that there is a hollow space, which measures about 60 to 100 meters (in length), at the bottom of Mount Mantap in the Punggye-ri site. So, should another nuke test occur, there is the possibility (of a collapse)."

When asked if an earthquake would trigger a release of radioactive materials, Nam said, "Should it sink, there is a possibility."

Nam's comment comes one day after the Hong Kong-based South China Morning Post reported that Chinese geologists warned a North Korean delegation last month of a possible implosion at the North's nuclear test facility.