North Korea appears to have blown up tunnels at its only nuclear test site, in a move to reduce regional tensions.

Foreign journalists at the Punggye-ri nuclear testing site in the north-east said they witnessed a huge explosion.

Pyongyang offered to scrap the site earlier this year as part of a diplomatic rapprochement with South Korea and the US.

But scientists believe it partially collapsed after the last test in September 2017, rendering it unusable.

Independent inspectors were not allowed to attend the dismantling of the Punggye-ri site in the mountainous region of the country.

Three tunnels were collapsed in a series of explosions in front of about 20 handpicked international journalists.

Two blasts were reportedly carried out in the morning, and four in the afternoon.

Sky News' Tom Cheshire was among the journalists present. He said the doors to the tunnels were "theatrically rigged" with "wires everywhere".

"We hiked up into the mountains and watched the detonation from about 500m away (550 yards)," he was quoted by Sky News as saying.

"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."

North Korea has conducted six nuclear tests since 2006 in a system of tunnels dug below Mount Mantap,

It is thought to have been the North's main nuclear facility and until now the only active nuclear testing site in the world.

Test devices are buried deep at the end of the tunnels, which end in a hook.

The tunnel gets backfilled to prevent radioactive leakage and then the device is detonated.