"The South Korean government said it was trying to confirm the report of an explosion at 11 a.m. on Thursday in Yanggang province near the border with China.
"We understand that a mushroom-shaped cloud about 3.5- to 4-kilometer (2.2 miles to 2.5 miles) in diameter was monitored during the explosion," the source in Seoul told Yonhap. Yonhap described the source as "reliable."
Very early report, my guess is this is a conventional explosion or a related accident, not a nuke.
(Yes, Im back)