What was left of Hiroshima after US forces dropped the first atomic bomb ever used in warfare, in August 1945.

Hiroshima blast times one thousand

North Korea's latest blast was somewhere between four and 16 times as powerful as the country's previous largest explosion, but well short of the worst imaginable nuclear explosion.

President Donald Trump called an emergency meeting of national security advisers.

US warns North Korea of 'massive' war

The Trump administration warned of a potential "massive military response" against North Korea and threatened to cut off China from the US economy after Pyongyang's nuclear weapon test.

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