Fears of radiation leak after North Korean tunnel collapse

An expert has warned of a possible radiation leak at a North Korean nuclear test site after a tunnel collapse at the facility reportedly killed about 200 people.

The tunnel cave-in at the Punggye-ri test facility, first reported by Japanese media, is believed to have been caused by destabilisation after North Korea detonated a powerful hydrogen bomb test.

The test, which received international condemnation, unleashed a powerful 6.3 magnitude tremor.

The bomb was thought to have had a power range from 50 to 120 kilotonnes making it at least three times as powerful as the bomb that destroyed Hiroshima at the end of World War II.

On Monday, South Korea weather agency chief Nam Jae-cheol told the country's parliamentarians further testing at Punggye-ri test could lead to the collapse of the nearby Mount Mantap and radiation leaks into the environment.

"Should [the Punggye-ri site] sink, there is a possibility" that hazardous radioactive gas could be released into the atmosphere, Nam told politicians.

“Based on our analysis of satellite imagery, we judge that there is a hollow space, which measures about 60 to 100 metres, at the bottom of Mount Mantap in the Punggye-ri site,” he said.

“So, should another nuke test occur, there is the possibility (of collapse).”

Concerned parliamentarians then asked Nam if there was a risk of radiation, reports the Yonhap news service.

He replied: "Should it sink, there is a possibility."

It is not yet clear exactly when the collapse occurred, but it is thought to be some time after North Korea conducted its sixth nuclear test at the site in September.

Chinese scientists have raised similar concerns, warning that nuclear fallout could spread across "an entire atmosphere" if the mountains did collapse, reports Yonhap News.

And a report by the Washington Post suggested that the massive scale of North Korea's nuclear test has "altered the geological structure of the land".

It explained that the 2200m-high Mount Mantap is suffering "tired mountain syndrome", characterised by quakes in an area not known for seismic activity.