Kim Jong-un only agreed to freeze his missile tests because his underground nuclear test site has collapsed, Chinese experts have suggested.

The North Korean dictator announced on Saturday he would halt nuke trials and intercontinental missile launches ahead of an expected summit with US President Donald Trump.

His regime also vowed to dismantle the atomic facility at Punggye-ri in the country's north east to 'transparently guarantee' the end of testing.

But the surprise announcement comes after reports last year of major earthquakes and landslides in the mountainous area in the wake of five test blasts carried out by the secretive state in recent years.

Kim Jong-un agreed to freeze his missile tests because his underground nuclear test has collapsed, Chinese experts have claimed

‹ Slide me › Satellite images appeared to show multiple landslides in the wake of the hydrogen bomb blast, with green mountains reduced to muddy hillsides. The mountain range is pictured days before the September 3, 2017 blast (left) and a day after (right) with discolouration caused by landslides

According to the South China Morning Post, two groups of Chinese experts say the military facility has collapsed 'putting China and other nearby nations at unprecedented risk of radioactive exposure'.

One of the experts said this could be the real reason behind Kim Jong-un's decision to end his missile and nuclear trials.

The tyrant had claimed that the freeze was because he had now successfully developed the country's arsenal, including miniaturising warheads to fit them on to rockets.

But Wen Lianxing, from the University of Science and Technology of China in Hefei, and his researchers have concluded that a major collapse took place at Kim's atomic site after the country's sixth nuclear test in September.

At the time, Japan estimated that the blast was measured at 120 kilotons, eight times the size of the US device that destroyed Hiroshima in 1945.

Satellite images appeared to show multiple landslides in the wake of the hydrogen bomb blast, with green mountains reduced to muddy hillsides.

Weeks later, unverified reports emerged that up to 200 workers may have been killed during the construction of a new tunnel at the site.

Wen's team said the September 3 trial had reduced the mountain to 'fragile fragments', with the heat from the blast 'vaporising' rocks and creating a huge space measuring 650ft in diameter, which was then filled by a landslide from the mountain above.

The surprise announcement comes after reports last year of major earthquakes and landslides in the mountainous area in the wake of five test blasts carried out by the secretive state in recent years. Satellite images appeared to show how there had been multiple landslides in the area

Pyongyang has made rapid technological progress in its weapons programmes under Kim, which has seen it subjected to increasingly strict sanctions by the UN Security Council, the United States, the European Union, South Korea and others

Three small earthquakes then hit nearby regions, it is claimed.

A second team of experts at Jilin Earthquake Agency and the China Earthquake Administration made similar findings, adding that the collapse created a 'chimney' that could potentially allow fallout to seep from the site.

Zhao Lianfeng, from the Institute of Earth Science at the Chinese Academy of Sciences in Beijing, said there was general agreement among experts that the site was 'wrecked' beyond repair, SCMP reported.

Chinese expert Hu Xingdou, who follows Pyongyang's nuke development, said Kim Jong-un may have been warned by Beijing amid fears the September test had increased the risk of an active volcano erupting on the China-North Korea border.

He said the collapse would have been a hammer blow to Kim Jong-un's nuclear ambitions with international sanctions meaning cash may not be readily available to resume tests any time soon.

Despite Kim's announcement over the weekend, he gave no indication Pyongyang might be willing to give up its nuclear weapons, or the missiles with which it can reach the mainland United States.

He said Kim offered no sign he might be willing to give up what he called the North's 'treasured sword', saying its possession of nuclear weapons was 'the firm guarantee by which our descendants can enjoy the most dignified and happiest life in the world'.

Kim's regime has vowed to dismantle the atomic facility at Punggye-ri (pictured) in the country's north east to 'transparently guarantee' the end of testing

Pyongyang has made rapid technological progress in its weapons programmes under Kim, which has seen it subjected to increasingly strict sanctions by the UN Security Council, the United States, the European Union, South Korea and others.

Last year it carried out its sixth nuclear blast, by far its most powerful to date, while Kim and Trump traded threats of war and personal insults as tensions ramped up.

Even when there was an extended pause in testing, US officials said that it could not be interpreted as a halt without an explicit statement from Pyongyang.

Kim told the Workers' Party meeting: 'A fresh climate of detente and peace is being created on the Korean peninsula and the region and dramatic changes are being made in the international political landscape.'

For years, the impoverished North has pursued a 'byungjin' policy of 'simultaneous development' of both the military and the economy.

But the leader said that as it was now a powerful state, 'the whole party and country' should concentrate on 'socialist economic construction'.

Several factors have driven the Korean rapprochement, including the North feeling that it can now negotiate from a position of strength, concern about the belligerence of the Trump administration, and the looming impact of sanctions.