About 200 people are feared dead in North Korea after underground tunnels at a nuclear test site that was feared to be unstable reportedly collapsed, crushing 100 people in the initial cave-in and 100 others when the tunnels again gave way on top of rescuers.

The collapse at the Punggye-ri test site on Oct. 10 occurred while people were doing construction on the underground tunnel, Japan’s Asahi TV reported, citing a source in North Korea. The television station also said North Korea’s sixth nuclear test on Sept. 3 most likely caused the tunnel to crumble and created serious damage in the region.

No officials have confirmed the Japanese TV station’s claims, but experts have feared for more than a month that the test site was on the verge of crumbling since the nuclear blast. North Korea said it detonated a hydrogen bomb, calling it a “perfect success.” It was the country’s most powerful bomb tested to date and the blast was reportedly 10 times more powerful than the nuclear bomb that was dropped over Hiroshima at the end of World War II.

The test triggered a 6.3-magnitude earthquake that day and multiple tremors have been detected from the area since then. Satellite images obtained by 38 North, which specializes in North Korea issues, showed several landslides occurred after the Sept. 3 test. Also a possible “collapse chimney crater” was seen on Mount Mantap, possibly caused by the underground tests.

It’s unclear if the mountain will collapse in the near future, but the report said there was “significant cracking” and “irreversible strain” on the land because of the nuclear test.

Some experts also said Mantap was suffering from “tired mountain syndrome” due to the stress on the ground, the Washington Post reported. Chinese scientists have also warned the mountain could collapse and release radiation. Radioactive xenon-133 was detected in South Korea after the test.

Additionally on Tuesday, North Korea rebuked Trump and the U.S., saying "the Trump group's vicious vituperation against the DPRK is an expression of their frustration, fear and horror,” according to a statement released by state-run Korean Central News Agency. The day before, the Hermit Kingdom blamed Trump’s “extreme, direct and long threats” for driving them to obtain "complete nuclear deterrence.”

“The U.S. has to ponder over the possible consequences,” the statement said.