HONG KONG • China has warned North Korea that further nuclear tests could blow the top off a mountain and spark a potential catastrophic collapse at the nuclear testing site, just 80km from the Chinese border, the South China Morning Post reported.

Researchers from the Chinese Academy of Sciences' Institute of Geology and Geophysics briefed a North Korean delegation in Beijing on Sept 20 on the threat of an implosion at the mountainous Punggye-ri nuclear facility, according to the report last Saturday, which cited senior Chinese geologist Zhai Mingguo.

The North Korean delegation was headed by Mr Lee Doh Sik, the director of the Geological Research Institute at the State Academy of Sciences, it said.

The paper cited scientists who attended the briefing as saying that the meeting was friendly. Details of the discussions were not revealed because they concerned "diplomatic affairs".

But two days after the briefing, North Korean Foreign Minister Ri Yong Ho announced at the United Nations in New York that Pyongyang might consider detonating a "most powerful" hydrogen bomb over the Pacific Ocean.

According to the paper, all five of North Korea's previous nuclear tests had been under the same mountain.