The government of North Korea conducts its fifth and reportedly biggest nuclear test. World leaders condemn the act, with South Korea calling it "maniacal recklessness".

North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korean Peninsula and borders China and Russia to the north at the Yalu (Amnok) and Tumen rivers, and South Korea to the south at the Korean Demilitarized Zone (DMZ). The country's western border is formed by the Yellow Sea, while its eastern border is defined by the Sea of Japan. North Korea, like South Korea, claims to be the sole legitimate government of the entire peninsula and adjacent islands. Pyongyang is the capital and largest city.

The government of North Korea conducted a nuclear detonation on 9 September 2016, the fifth since 2006, at the Punggye-ri Nuclear Test Site, approximately 50 kilometres northwest of Kilju City in Kilju County.

South Korea, officially the Republic of Korea (ROK), is a country in East Asia. It constitutes the southern half of the Korean Peninsula and borders North Korea along the Korean Demilitarized Zone, with the Yellow Sea to the west and the Sea of Japan to the east. Like North Korea, South Korea claims to be the sole legitimate government of the entire peninsula and adjacent islands. It has a population of about 52 million, of which half live in the Seoul Metropolitan Area, the ninth most populous metropolitan area in the world; other major cities include Busan, Daegu, and Incheon.