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An underground North Korean military facility used for nuclear tests collapsed earlier this month, Pyongyang revealed Tuesday.

The collapse occurred on October 10th at the Punggye-ri underground nuclear facility, 50 miles from the Chinese border, South Korea’s Yonhap media outlet reported.

According to a North Korean official, the collapse occurred during the construction of an underground tunnel.

The Punggye-ri facility is located underneath the southern slope of Mount Mantap. Recent thermonuclear weapons tests at the site are believed to be responsible for the collapse.

Roughly 100 people were trapped in the initial collapse, Asahi TV reported, with 100 more lost during failed rescue attempts.

On Monday, South Korean weather agency chief Nam Jae-Cheol told lawmakers that the Punggye-ri facility could collapse if used for further testing, the Associated Press reported.

Last month, just after North Korea confirmed it had tested a hydrogen bomb, Chinese scientists warned that he Punggye-ri facility was at risk.

Researchers claimed that an explosion at the facility could spread dangerous radiation across the entire hemisphere.

“China cannot sit and wait until the site implodes. Our instruments can detect nuclear fallout when it arrives, but it will be too late by then. There will be public panic and anger at the government for not taking action," a researcher at the country's Peking University told the South China Morning Post.

"The fallout can spread to an entire hemisphere," Institute of Atmospheric Physics Associate Researcher Lan Xiaoqing said.