Pyongyang had announced that it would "completely" take apart the Punggye-ri facility in the country's northeast, inviting some foreign journalists to witness the destruction.

Reporters at the scene described a series of explosions throughout the day, three of them in entry tunnels to the underground facility, followed by blasts that demolished a nearby barracks and other structures.

"There was a huge explosion, you could feel it. Dust came at you, the heat came at you. It was extremely loud," Tom Cheshire, a journalist for Sky News who was among those invited to attend the ceremony, wrote on the British broadcaster's website.

The Punggye-ri test facility is buried inside a mountain in North Hamgyong province, near the border with China and is North Korea's only known nuclear test site.

It has been the staging ground for all six of the North's nuclear tests, including its latest and by far most powerful one in September last year, which Pyongyang said was an H-bomb.

- Concession or stunt? -

Experts are divided over whether the demolition will render the site useless. Sceptics say the facility has already outlived its usefulness with six successful nuclear tests in the bag and can be quickly rebuilt if needed.

North Korea did not invite any independent observers from overseas.

But others say the fact that North Korea agreed to destroy the site without preconditions and without asking for something in return from Washington suggests the regime is serious about change.

Koh Yu-hwan, a North Korea expert at Dongguk University, said the demolition "cannot be dismissed as a media stunt".

"It is significant that North Korea has backed up its commitment to denuclearisation with concrete action," he told AFP.

"This move heightens the likelihood of the US-North Korea summit taking place as scheduled."

Trump is due to meet his North Korean counterpart Kim Jong Un in Singapore on June 12 for high stakes talks aimed at ridding the reclusive state of its newly acquired nuclear weapons and improving ties after decades of animosity.

The summit announcement came after months of unusually cordial diplomacy between the historic foes brokered by South Korea.

But the newfound bonhomie and the meeting's potential success has been thrown into doubt in recent days with both Washington and Pyongyang raising the prospect of cancelling the talks and trading threats.

The latest broadside from North Korean came from a minister who called US Vice President Mike Pence "stupid and ignorant" for comments he made comparing the Pyongyang regime to Libya's Moamer Khadafi, who gave up his atomic weapons but was killed years later by US-backed rebels.

- Gulf in expectations -

Trump has said a final say on whether the summit will go ahead is likely to come "next week" but has touted the talks as a golden opportunity for Pyongyang.

"We will see what happens. There is a good chance. And it would be a great thing for North Korea," he told Fox News in an interview recorded before the nuclear test site demolition.

Politically, Trump has invested heavily in the success of the planned summit, so privately most US officials, as well as outside observers, believe it will go ahead.

Hand-picked US aides travelled to Singapore this week where they are expected to meet their North Korean counterparts and iron out details of the meeting.

But as the date draws nearer, the gulf in expectations between the two sides is coming into sharp relief.

Washington has made it clear it wants to see the "complete, verifiable and irreversible denuclearisation" of the North.

But Pyongyang has vowed it will never give up its nuclear deterrence until it feels safe from what it terms US aggression.

"I would like to have it (denuclearisation) done immediately," Trump told Fox. "Physically, a phase-in may be necessary," he added, leaving a window open for negotiating a more gradual disarmament.

A handful of foreign journalists from China, the US, Britain, Russia and South Korea were invited to attend the demolition ceremony.

Their journey to reach the remote site involved some 14 hours of travelling by train, bus and finally a short hike -- a vivid illustration of the impoverished country's notoriously decrepit infrastructure.

Agence France-Presse is one of a number of major media organisations not invited to cover the demolition.