Itsuo Inouye/Associated Press

Women in Tokyo read copies of a Japanese newspaper reporting North Korea's nuclear test.

Jon Chol Jin/Associated Press

A North Korean state television broadcaster announced the nuclear test on a large television screen in Pyongyang.

NORTH KOREAN TVAFP/Getty Images

North Koreans in Pyongyang celebrated as they watched the announcement.

GEORG HOCHMUTH/EPA

The international nuclear test monitoring agency CTBTO in Vienna, Austria, monitored the nuclear detonation.

DIETER NAGL/AFP/Getty Images

A Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) poster details previous North Korea nuclear tests.

Associated Press

A North Korean soldier patrolled the river bank of the North Korean town of Sinuiju, opposite the Chinese city of Dandong.

Ahn Young-joon/Associated Press

South Korean soldiers conducted an exercise near the demilitarized zone of Panmunjom in Pajuon Tuesday.

Lee Jin-man/Associated Press

A South Korean soldier watched a TV screen reporting seismic waves from North Korea's nuclear test.

HEINZ-PETER BADER/REUTERS

The seismic magnitude of the blast was roughly twice as large as that of a 2009 nuclear test in the country, the CTBTO said.

Chung Sung-Jun/Getty Images

South Korean conservative protesters participated in a rally against North Korea's nuclear test on Tuesday.