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At least 200 people have been killed at Kim Jong-un's nuclear test site in North Korea after a tunnel collapsed.

A news agency quoted a North Korean official as saying that a collapse occurred during the construction of an underground tunnel at the Punggye-ri nuclear test site in the northeast of North Korea on October 10.

According to the report, 100 people were trapped in underground tunnels, and a further collapse occurred during the rescue operation, suggesting that a total of 200 people may have been killed.

The accident is due to the weakening of the surrounding grounds due to the sixth nuclear test conducted here on September 3, TV Asahi reported.

(Image: US-Korea Institute at SAIS) (Image: REX/Shutterstock)

The blast last month was measured at a magnitude of 6.3., which said to have been the biggest blast yet.

It was reported after the test that new radar satellite images showed the explosion had been powerful enough to sink an 85-acre area of the mountain above tunnels where the test likely took place.

Jeffrey Lewis, East Asia program head at California's James Martin Center for Nonproliferation Studies, wrote there had been “significant changes at Mount Mantap’s peak elevation", the Washington Post reported.

(Image: Getty) (Image: REUTERS)

"Before the test, Mount Mantap was 2,205 meters high; the mountain has since diminished in height.

"You can see that the explosion visibly displaces the mountain, which demonstrates both how large the explosion was but also that it occurred in the same tunnel complex as the preceding four nuclear tests."

Writing at Arms Control Wonk on September 13, Lewis said: "Similar images were collected before and after North Korea’s January 2016 nuclear test but showed no such ground disturbance."

The Korea Meteorological Administration said in a National Assembly audit on October 30 that: "There seems to be a cavity of 60 meters to 100 meters under the mountain where there is a nuclear test site."

It also reportedly pointed out that there was a possibility that radioactive substances may leak out in the future if nuclear tests are conducted.

(Image: AFP)

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It was reported earlier this month that a tremors and landslides near the base meant the country's sixth and largest blast had destabilized the region.

The Punggye-ri nuclear site was considered at the time to have come to the end of its run, Newsweek reported.

(Image: Getty)

Korea Seismological Institute head researcher Kim So-gu had told the website: "The explosion from the September 3 test had such power that the existing tunnels within the underground testing site might have caved in.

"I think the Punggye-ri region is now pretty saturated.

"If it goes ahead with another test in this area, it could risk radioactive pollution."

There were also fears that testing in the area could trigger an eruption of a nearby volcano.