“SEOUL, Sept 12 (Reuters) – A mushroom cloud up to 4 km (about 2.5 miles) in diameter was seen after an explosion in a remote area of North Korea near the border with China, Yonhap news agency reported on Sunday, quoting sources in Beijing.”

Details are sketchy at best, but the explosion is said to have been larger than the explosion along the Chinese border last April. Apparently it was noted by a passing satalite.