Experts estimate that as many as 200 North Koreans have been killed in the collapse of a nuclear test site.

North Korea's nuclear test site, Mount Mantap, has been structurally unsound since the nation began testing their nuclear missiles under the mountain. Now, sources inside the country say that one of the tunnels near the test site has collapsed, according to The Telegraph. Allegedly, an initial collapse killed around 100 workers; when an additional 100 were sent in to rescue them, they too were killed.

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North Korea claims that the sixth test, which took place on Sept. 3, was a test of a hydrogen bomb. Officials estimate from the size of the quake that the explosion was at least 17 times as powerful as the bomb that the United States dropped on Hiroshima in 1945, The Washington Post reports. The mountain has been suffering from a condition referred to as "tired mountain syndrome." But the possible collapse of the tunnels may not have been the first casualties caused by North Korea's nuclear missile tests–there have been multiple landslides from the mountain as well, the LA Times reports.

If the tunnels actually did collapse, there's little chance that the nation's state media would report on the incident; the Telegraph cites Japanese media in their report. Also, North Koreans should be wary of their tunnels collapsing, if they actually do go down, then the resulting radioactive fallout could be deadly to surrounding civilians.