North Korean nuke test tunnel caves in, killing 200 workers

As many as 200 North Korean labourers were killed when underground workings at the regime's nuclear test site collapsed.

Sources in North Korea told Japan's Asahi TV that a tunnel being excavated by about 100 workers at the Punggye-ri test site collapsed in October.

Another 100 labourers sent to rescue their colleagues were reportedly killed when the tunnel collapsed a second time.

An exact date for the disaster has not been provided, but it comes shortly after North Korea conducted its sixth - and most powerful - underground nuclear test at the site.

North Korea claims the September 3 test beneath Mount Mantap was of a hydrogen bomb, with monitors suggesting the detonation was equivalent to an earthquake with a magnitude of 6.1 on the Richter scale.

Some analysts put the yield of the weapon as high as 280 kilotons, while seismologists picked up signs of underground collapses in the hours and days after the blast.

There has been speculation about the site suffering "tired mountain syndrome" - which arises from underground nuclear testing - but there have been no indications of it being abandoned for future nuclear tests.

Satellite images of Punggye-ri taken immediately after the test revealed significant damage to surface features, including landslips.

On October 17 a study published by the US-Korea Institute at Johns Hopkins University and published on the 38 North website suggested the sixth underground test at the site had caused "substantial damage to the existing tunnel network under Mount Mantap".

Nam Jae-chol, the head of South Korea's Meteorological Administration, warned in testimony before parliament on Monday that further tests at Punggye-ri could cause the mountain to collapse and release radioactivity into the environment.

"Based on our analysis of satellite imagery, we judge that there is a hollow space about 60m by 100m beneath Mount Matap," he said.

"Should another nuclear test take place, there is a possibility [of a collapse]."

Chinese scientists have issued similar warnings, suggesting that nuclear fallout could spread across "an entire hemisphere" if the mountain did collapse.