From Yonhap News:
(4th LD) N. Korea demolishes nuclear test site
2018/05/24 20:42
(ATTN: UPDATES with details; CLARIFIES tunnel names in paras 2-7)
PUNGGYE-RI, May 24 (Joint Press Corps-Yonhap) -- North Korea destroyed its only known nuclear test site with a series of explosions over several hours on Thursday, taking an initial step toward denuclearization, according to South Korean journalists visiting the area.
The North dynamited the North Portal, also referred to as Tunnel No. 2, at Punggye-ri, a northeastern remote area, at around 11 a.m., they said in a brief pool report delivered by phone.
Two other tunnels were destroyed at 2:17 p.m., followed by the explosion of barracks, observation towers and other facilities on the ground.
The blasts ended at 4:17 p.m., the journalists said without clarifying whether Tunnel No. 1, or the East Portal, was removed as well. Among the four tunnels in the zone, the East Portal was evidently abandoned earlier, according to 38 North, a U.S.-based website.