The demolition on Thursday was deep in the mountains in the northeast portion of North Korea, the AP reported.
North Korea's decision to shutter the site was considered by international observers to be a good omen leading up to a potential meeting between Kim Jong Un and U.S. President Donald Trump in Singapore next month.
Journalists from around the world flew from Beijing to Wonsan, on the east coast of North Korea, Tuesday and were taken on a long journey to the nuclear site near the village of Punggye-ri.
North Korean state media previously reported the dismantlement process will involve "collapsing all of its tunnels with explosions, blocking its entrances and removing all observation facilities, research buildings and security posts" and that foreign media were invited to cover the event to show the process in a "transparent manner."
The apparent dismantlement came just hours after the country threatened to pull out of the planned summit with the U.S. over remarks from Vice President Mike Pence, who compared North Korea to Libya, which abandoned its nuclear program early on in hopes of striking a deal with the US only to have its leader ousted and killed years later.
Choe Son Hui, a vice minister in the North Korean Foreign Ministry, called the comments "unbridled and impudent."
“We could surmise more than enough what a political dummy he is as he is trying to compare the DPRK, a nuclear weapon state, to Libya that had simply installed a few items of equipment and fiddled around with them,” KCNA quoted Choe as saying Thursday. "We will neither beg the U.S. for dialogue nor take the trouble to persuade them if they do not want to sit together with us.
"Whether the U.S. will meet us at a meeting room or encounter us at nuclear-to-nuclear showdown is entirely dependent upon the decision and behavior of the United States," she added.
ABC News’ Karson Yiu and Ben Gittleson contributed to this report.