The Sun The Punggye-ri test site in North Korea is carved deep into Mount Mantap, as these file images show
The disaster has prompted fears of a massive radioactive leak which could spark a Chernobyl- or Fukushima-style disaster.
A North Korean official said the collapse happened during the construction of an underground tunnel, South Korea’s Yonhap news agency reports.
Some 100 people are said to have been trapped by the initial tunnel collapse, with a further 100 lost in a second collapse during a rescue operation, Asahi reported Tuesday.
Lee Eugene, a spokeswoman at South Korea's unification ministry, said: "We are aware of the report but do not know anything about it."
The accident is believed to have been caused by Kim Joing-un’s sixth nuclear test which weakened the mountain, according to the report.
