North Korea has carried out the apparent demolition of its main nuclear testing facility.

International journalists - mostly TV reporters - witnessed the much-heralded closure of the Punggye-ri nuclear test site.

Tunnels and observation cabins were said to be among the structures visibly destroyed.

Reporters said they had travelled 12 hours overnight in a train with 'blacked out windows' before reaching the site in the north of the country to view the apparent demolition.

Sky News Asia correspondent Tom Cheshire was among the journalists who witnessed the closure.

He said: "We hiked up into the mountains and watched the detonation from about 500 metres away.

"They counted it down - three, two, one. There was a huge explosion, you could feel it.

"Dust came at you, the heat came at you. It was extremely loud. It blew an observation cabin made out of wood to complete smithereens."

CNN journalists, meanwhile, reported watching "a succession of explosions" before being allowed inspect the damage.

"Each tunnel was caved in, with rubble blocking the entrance," they reported.

Chinese geologists had previously said they believed the nuclear testing site had collapsed under the stress of five successive bomb tests.

Kim Jong Un had pledged to publicly close the test site, with both North and South Korea having recently pledged to work towards the 'complete denuclearisation' of the peninsula.

It also comes ahead of the planned summit between Mr Kim and Donald Trump next month - although both sides have cast some doubt over the meeting in recent days.