Mount Mantap, North Korea. (Image: Google Earth)

As many as 200 workers were killed after a tunnel collapsed at North Korea’s underground nuclear test site, according to unconfirmed reports by Japanese broadcaster TV Asahi. The accident is presumed to have happened in early September following the country’s most recent test of a hydrogen bomb, which may have compromised the geological strength of the mountain.

According to the report, the tunnel collapsed at North Korea’s Punggye-ri nuclear test site sometime around September 10th, which is about a week after the September 3rd test of a hydrogen bomb—the most powerful nuclear explosion ever achieved by the country. TV Asahi said it received the tip from unnamed North Korean sources who are familiar with the situation, and that the incident happened during construction of an underground tunnel at the nuclear test site in northeast North Korea.

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Around a hundred workers were killed during an initial collapse, but many others were killed during the rescue attempt during a second collapse, “raising the possibility that more than 200 people died together,” stated the broadcaster.

Screengrab from the TV Asahi report.

The incident is still unconfirmed, but experts say the ground may have been loosened following the most recent nuclear test in early September. At the time, South Korea’s Meteorological Agency said there “seems to be a cavity of 60 meters to 100 meters [200 to 330 feet] under the mountain where there is a nuclear test site,” warning that radioactive substances might start to leak out if more tests are conducted within Mount Mantap, a 7,200-foot high-peak.

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This news comes less than two weeks after a Washington Post report claimed that North Korea’s underground nuclear tests are so big they’ve “altered the geological structure of the land” and that it’s suffering from “tired mountain syndrome.”

“What we are seeing from North Korea looks like some kind of stress in the ground,” Columbia University seismologist Paul G. Richards told WaPo. “In that part of the world, there were stresses in the ground, but the explosions have shaken them up.”

Chinese scientists also chimed in, warning that further nuclear tests could cause the mountain to collapse and release radiation caused by the tests.

We’ll update this post as we learn more.

[Reuters, TV Asahi]