North Korea has conducted all six of its nuclear tests at the Punggye-ri site, which consists of tunnels dug beneath Mount Mantap in the northeast of the country.
A small group of international media selected by North Korea was on hand to witness the demolition, which Pyongyang says is proof of its commitment to end nuclear testing.
The destruction of the site began at about 11 a.m. with the blowing up and collapsing of a tunnel and an observation post.
South Korean media described how North Korean authorities called out to media to ask if they were ready to film the first blast. They then counted down.
“With a heavy boom that shook Mount Mantap, dirt and broken rocks spilled out from the entrance,” South Korean media reported.
After some time, another tunnel and other facilities were destroyed, then a third tunnel and another observation post. About five hours after the operation began, two military barracks were demolished, South Korean media said, according to Reuters.
The North Korean offer to scrap the test site has been seen as a major concession in months of easing tension between it, on the one hand, and South Korea and the United States on the other.