More than 200 people were killed after a tunnel collapsed at a nuclear test site in North Korea after an atomic test, it has emerged.

The collapse happened at the Punggye-ri nuclear test site in the north-east of the country on October 10, Japanese broadcaster TV Asahi said on Tuesday, citing unnamed sources familiar with the situation.

About 100 workers at the nuclear site were affected by the initial collapse, the broadcaster said. A second collapse during a rescue operation meant it was possible the death toll could have exceeded 200, it added.

The disaster has also prompted fears of a massive radioactive leak which could spark a Fukushima-style disaster.

Experts have said a series of tremors and landslides near the nuclear test base probably mean the country’s sixth and largest blast on September 3 has destabilised the region, and the Punggye-ri nuclear site may not be used for much longer to test nuclear weapons.