How a hydrogen bomb differs from an atomic device

North Korean leader Kim Jong Un with what the regime said was a hydrogen device. Photo / AP

North Korea tested what it said was a hydrogen nuclear bomb yesterday.

1 Atomic bombs and hydrogen bombs are both nuclear weapons, but hydrogen bomb blasts are up to 1,000 times more powerful.

2 Atomic bombs, like the ones the US dropped on Japan hoping to end WWII, get their power from nuclear fission - splitting large atoms into smaller ones.

3 Hydrogen bombs get their power from a two-stage reaction: firstly fission, which splits atoms, then fusion, which melds two or more atoms to create larger ones. This two stage process is often referred to as a thermonuclear reaction.

4 The atomic bomb dropped on Hiroshima unleased the equivalent force of 15 kilotons of TNT. By comparison, the first hydrogen bomb tested by the US had the equivalent power of 10,000 kilotons of TNT.

5 The Hiroshima bombing killed an estimated 140,000 people, with 74,000 others believed to have died when a second atomic bomb was dropped on Nagasaki days later.

6 North Korea says the hydrogen bomb it says it tested yesterday is designed to be mounted on intercontinental ballistic missiles.

7 US President Donald Trump has indicated he's prepared to respond in kind to a nuclear strike by North Korea, saying Washington will use "the full range of diplomatic, conventional, and nuclear capabilities at our disposal".

- AAP