North Korea draws criticism and threats over it's continued development of nuclear arms - this time a hydrogen bomb test that measured on the Richter scale.
North Korea claims to have successfully tested a hydrogen bomb for the first time in a move that alarmed the world.
The test sparked a furious response from the US, Japan, China and South Korea, which conducted a ballistic missile exercise in response to Pyongyang's claim that it had successfullytested a miniaturised hydrogen bomb.
Experts have expressed alarm at the technology but also how quickly Pyongyang has accelerated its nuclear weapons program.
North Korea's state media claimed it tested the bomb, which was capable of being loaded into an ICBM in a major game changer.
If it launched one on any western city, thousands would die and infrastructure would be destroyed.
An atomic bomb generates energy through the process of nuclear fission where the nucleus of an atom splits.
The hydrogen bomb, also called a thermonuclear bomb, is more powerful and uses fusion - or atomic nuclei coming together - to produce explosive energy.
Both are capable of making a deadly impact.
Mr Hallam, a member of the People for Nuclear Disarmament and the co-founder of the Human Survival Project, said he believed an attack on a major Australian city was unlikely.
He said Pine Gap - a nuclear commander controlled installation - was more of a target, as were major built-up cities such as Seoul and Tokyo.
Mr Hallam said a bomb dropped over Sydney's Centrepoint tower would wipe out the city and only those west of Homebush would "have any chance of survival".
Deadly, destructive
Mr Hallam said whether Pyongyang tested a H-bomb or gas-boosted bomb remained a huge concern.
Either would be much more destructive than that dropped on the Japanese cities of Hiroshima and Nagasaki at the end of World War II.
"North Korea is playing games," Mr Hallam said.
"Every time there's universal prediction they will test a bomb they don't.
"But the surprising thing in this is how much bigger this test was."
Mr Hallam warned the world was playing a very dangerous game by antagonising North Korea, which was determined to achieve its nuclear ambition despite sanctions, which simply weren't working.
"Blind Freddie will tell you sanctions will not be effective," he said.
"It will only incentive them to work harder and quicker to get what they want.
"We just don't get it, we need to back off, calm down and talk and then talk some more.
The photo released (of Sunday's test) is pretty convincing, it has been sent to us for a reason."
The precise strength of the underground nuclear explosion had yet to be determined.
However, according to South Korea's weather agency, the artificial earthquake caused by the explosion was five times to six times stronger than tremors generated by the North's previous five nuclear tests.
Sunday's detonation builds on recent North Korean advances that include test launches in July of two intercontinental ballistic missiles (ICBMs) that are believed to be capable of reaching the mainland US.
Tremors caused were at least 10 times as powerful as the last time Pyongyang exploded an atomic bomb a year ago, the Japan Meteorological Agency (JMA) said.
The Korea Meteorological Administration estimated that the nuclear blast yield of the presumed test was between 50 to 60 kilotons, or five to six times stronger than the North Korea's test in September 2016.
However, the Arms Control Association said the explosion appeared to produce a yield in excess of 100 kilotons of TNT equivalent.
