North Korea’s mountain nuclear test site has collapsed — leading one researcher to suggest that is why Kim Jong Un shut it down and announced he would freeze missile testing, according to reports.

The dictator announced Saturday that he would halt nuclear and intercontinental ballistic missile tests ahead of an inter-Korean summit Friday and an expected meeting with President Trump by June.

He also said he would close the Punggye-ri facility under Mount Mantap — where the last five of the hermit kingdom’s six nuclear tests were carried out — because Pyongyang had reached its weapons development goals, the South China Morning Post reported.

But Chinese seismologists, led by researchers at the University of Science and Technology of China in Hefei, said a cavity inside the mountain has collapsed.

A research team led by geologist Wen Lianxing concluded that the collapse occurred after a detonation of Pyongyang’s most powerful thermonuclear warhead in a tunnel about 2,300 feet under the mountain’s peak, according to the news outlet.

The blast vaporized surrounding rocks and opened up a chasm estimated to be about 650 feet in diameter, according to Wen’s team, which analyzed data collected from about 2,000 seismic stations.

According to the researchers, radioactive dust could have escaped through fissures in the damaged mountain.

The experts warned that another explosion at the same site and with a similar yield to the 100-kiloton Sept. 3 blast could cause an “environmental catastrophe,” according to the Wall Street Journal.

“It is necessary to continue monitoring possible leaks of radioactive materials caused by the collapse incident,” Wen’s team said in a statement about the findings, which will be published by peer-reviewed journal Geophysical Research Letters.

Wen, a seismology professor at Stony Brook University, said the findings will not include wording that Mount Mantap is unusable for future tests, according to the Wall Street Journal.

A separate research team led by Liu Junqing at the Jilin Earthquake Agency with the China Earthquake Administration in Changchun reached similar conclusions.

That study said the “explosion created a cavity and a damaged ‘chimney’ of rocks above it.”

The “rock collapse … was for the first time documented in North Korea’s test site,” Liu’s team wrote in a report published last month in the American Geophysical Union’s journal.

One co-author, Professor Li Li of the China Earthquake Administration’s Institute of Geophysics, told the Wall Street Journal she thought it is possible that the site could be used for further tests.

North Korea experts at Johns Hopkins University’s US-Korea Institute said in a report published Monday that Punggye-ri was still fully operational.

The area at Mount Mantap was apparently abandoned, but two other parts appeared to be operational, they said on the institute’s 38 North website.

“Whether that will stay an option will depend on reaching verifiable agreements that build on Pyongyang’s pledge to shut down the facility,” the report said.