North Korea has raised the terrifying spectre of a hydrogen bomb being detonated in the Pacific Ocean as Kim Jong-un made an unprecedented personal statement in which he lambasted Donald Trump as a “mentally deranged dotard”.

The US president fired back calling the North Korean leader a “madman” as tensions escalated to a frightening new level, with Japan bracing for a nuclear-armed missile flying over its territory.

Analysts view with dread the prospect of such a missile exploding accidently over the close US ally, a scenario which would likely lead to nuclear conflict in north-east Asia.

The threat came amid a dramatic escalation in the war of words between Washington and Pyongyang with Mr Kim saying Mr Trump would "pay dearly" for warning that he would destroy North Korea.

“We will consider with seriousness taking a corresponding, highest level of hard-line countermeasure in history,” he said.

“Action is the best option in treating the dotard who, hard of hearing, is uttering only what he wants to say.”