North Korea said Thursday it has "completely" dismantled its only known nuclear test site in Punggye-ri in the presence of foreign reporters as promised, hours before U.S. President Donald Trump abruptly called off next month's planned Washington-Pyongyang summit.

It said in a statement that the demolition was conducted in such a manner as to "make all the tunnels of the test ground collapse by explosion and completely close the tunnel entrances."

The foreign journalists who visited the Punggye-ri test site in the country's northeast reported that three underground tunnels, observation buildings and other facilities used for nuclear testing were blown up.

(North Korea released Friday photos of the dismantling of its nuclear test site.)

The reporters said they witnessed the explosions from observation decks about 500 meters away.

"There was a huge explosion, you could feel it. Dust came at you, the heat came at you. It was extremely loud," a reporter from Britain's Sky News said.

One of the three tunnels was demolished at 11 a.m. and the other two were done about 2 p.m., they said, adding that the explosions, carried out over several hours, ended after 4 p.m.

"There were neither leakage of radioactive materials nor any adverse impact on the surrounding ecological environment," the North's Nuclear Weapons Institute, which released the statement, said.

"The discontinuance of the nuclear test is an important process moving toward global nuclear disarmament," the statement carried by the country's official Korean Central News Agency said.

North Korea allowing the foreign journalists to conduct on-the-spot coverage of the demolition was seen as a sign of goodwill from Kim, but there was skepticism that the event might be only a "political show."

Experts such as those from the International Atomic Energy Agency were not invited to observe the dismantling, raising concern that the actual condition of the test site after demolition will not be revealed.

[Photos by KCNA/Kyodo]

At his summit with South Korean President Moon Jae In on April 27, Kim pledged to shut down the nuclear test site in May and disclose its dismantlement to foreign experts and media to ensure transparency.

At a plenary meeting of the Central Committee of the Worker's Party of Korea last month, North Korea decided to dismantle the test site, as well as suspend nuclear and missile tests.

"The mission of the northern nuclear test ground has thus come to an end," Kim, chairman of the ruling party, was quoted as saying by KCNA.

Kim was believed to have started to commit "complete" denuclearization on the divided peninsula to gain security guarantees and other returns from Washington.

Trump, however, canceled on Thursday the summit with Kim, criticizing recent hostile remarks by North Korea.