North Korea nuclear test site has collapsed, say Chinese scientists

North Korea's underground nuclear test site has partially collapsed, according to Chinese geologists, prompting fears that radioactive materials may have leaked from the area.

North Korea has conducted underground tests at Punggye-ri in the country's mountainous north since 2009.

Repeated tests are now believed to have triggered a series of small earthquakes in September and October 2017, according to the University of Science and Technology of China, which monitors North Korean nuclear tests.

The university published its findings this week after studying earthquake records and said North Korea's test site has at least partially collapsed. It also warned that it will be necessary to monitor for possible leakage of radioactive materials.

However, experts from the US-North Korea Institute at John Hopkins University cast doubt on the finding. According to a post on the 38 North news portal, despite signs that the site has gone quiet, there still seem to be tunnel areas that are still viable for testing.

"There is no basis to conclude that the Punggye-ri nuclear test site is no longer viable for future nuclear testing," concludes the post.

North Korea leader Kim Jong Un last week announced that he would shut down a nuclear test site as part of his promise to end the country's nuclear programme ahead of a summit with South Korea this week.