Photo taken on May 24, 2018 shows explosions of the No. 2 tunnel at the nuclear test site of Punggye-ri, the Democratic People's Republic of Korea. The Democratic People's Republic of Korea has confirmed the demolition of its nuclear test site at Punggye-ri on Thursday, saying that all the tunnels have been collapsed by explosions and their entrances completely closed, according to the Korean Central News Agency (KCNA). (Xinhua/Cheng Dayu)

PYONGYANG, May 24 (Xinhua) -- The Democratic People's Republic of Korea (DPRK) has confirmed the demolition of its nuclear test site at Punggye-ri Thursday, saying all its tunnels have been collapsed by explosions and their entrances completely closed, the Korean Central News Agency (KCNA) said.

The Nuclear Weapons Institute of the DPRK issued a statement saying that a ceremony was held "for completely dismantling the northern nuclear test ground ... to ensure transparency of the discontinuance of nuclear tests."

"Dismantling the nuclear test ground was done in such a way as to make all the tunnels of the test ground collapse by explosion and completely close the tunnel entrances, and at the same time, explode some guard facilities and observation posts on the site," the statement said.

The statement also said it has been confirmed that there was neither leakage of radio-active materials nor any adverse impact on the surrounding ecological environment.

A complete closure of the area surrounding the nuclear test ground will come after a successive removal of all ground observation facilities, research institutes and structures of guard units, and withdrawal of staff concerned, it said.

The three tunnels of the test site were blown up by 16:00 local time (0700 GMT), according to Xinhua reporters at the site.

Pyongyang invited journalists from China, Russia, the United States, South Korea and Britain to witness the site's dismantlement.

The DPRK conducted six nuclear tests at Punggye-ri between October 2006 and September 2017.

According to an official from the Nuclear Weapons Institute, Thursday's demolition was done to the remaining three tunnels at the test site, on the northern, western and southern sides, respectively.

The official told international journalists invited to witness the closure that the north tunnel was used to carry out the country's second to sixth nuclear tests conducted between 2009 and 2017, and that the west and south tunnels had been completed and could have been used to conduct further tests at any time.

The east tunnel, according to the official, had already been abandoned and blown up after the first nuclear test in 2006.

The Third Plenary Meeting of the Seventh Central Committee of the ruling Workers' Party of Korea decided last month that the country will discontinue its nuclear tests and intercontinental ballistic rocket test-firings from April 21.