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Scientists from Beijing believe the Punggye-ri nuclear facility is unstable and that just one more explosion could blow the top off of Mount Mantap, beneath which all six of North Korea's nuclear tests thave been conducted.

That could lead to the mountain collapsing, causing radioactive waste to escape and blow aross the border into China just 50 miles away.

Researchers from the Chinese Academy of Sciences’ Institute of Geology and Geophysics warned Pyongyang delegates of the risk during a briefing in Beijing soon after North Korea's last nuclear test on September 3, according ot the South China Morning Post.

Tellingly, the meeting occured two days before North Korean Foreign Minister Ri Yong-ho told reporters at the United Nations Assembly in New York Pyongyang was considering conducting a hydrogen bomb test over the Pacific Ocean.