North Korea said Wednesday it conducted a "successful" hydrogen bomb test.
The announcement on state television came less than a month after North Korean leader Kim Jon Un claimed his country had developed a hydrogen bomb. The United States and others quickly discounted that claim.
A map locating North Korea's nuclear facilities.
A hydrogen bomb, also known as a thermonuclear bomb, is far more powerful than a atomic bomb.
North Korea conducted three previous nuclear tests in 2006, 2009 and 2013. All of them took place at the Punggye-ri site, the same area where several monitoring agencies detected man-made earthquake activity on Wednesday morning.
The test prompted emergency national security meetings in South Korea and Japan.
Japanese Prime Minister Shinzo Abe condemned North Korea's test, calling it a serious threat to Japan's national security.
North Koreans gather at Kim Il Sung Square, following their leader Kim Jong Un's new year address in Pyongyang, North Korea, Tuesday, Jan. 5, 2016.