North Korea could detonate a powerful hydrogen bomb over the Pacific Ocean as a response to the US President Donald Trump's latest threat at the UN, warned Pyongyang's foreign minister.

Foreign Minister Ri Yong Ho's threat comes shortly after the country's Supreme Leader Kim Jong-un promised the US would "pay dearly" for threatening to "totally destroy" North Korea.

Ri, the North's top diplomat, was speaking to reporters in New York, where he has travelled to speak at the UN General Assembly. He warned Pyongyang could take its "highest-level" action against the US if the country's leadership decides.

"It could be the most powerful detonation of an H-bomb in the Pacific. We have no idea about what actions could be taken as it will be ordered by leader Kim Jong-un," said Ri.

The North had conducted its sixth and most powerful nuclear test on 3 September rattling regional and global powers. The hermit kingdom claimed it was a hydrogen bomb detonation – which is significantly powerful than an atomic bomb – though there is no independent confirmation on it as yet.

Ri's comments were preceded by a rare direct threat from Kim, who said he "will consider with seriousness exercising of a corresponding, highest level of hard-line countermeasure in history".

"I am now thinking hard about what response he could have expected when he allowed such eccentric words to trip off his tongue. I will surely and definitely tame the mentally deranged US dotard with fire," added Kim, according to the state news agency.

The foreign minister's threat of unprecedented proportions triggered some quick reactions from countries such as Australia and Japan.

"That would be a disaster beyond compare for the region, for the people of North Korea, who have no dog in this fight, who are just trying to feed themselves," Australia's Deputy Prime Minister Barnaby Joyce told reporters in Perth.

Echoing a similar stance, Japan's Chief Cabinet Secretary Yoshihide Suga emphasised it was "absolutely unacceptable" for North Korea to make such belligerent remarks.

North Korea Nuclear Weapon Kim Jong-un
North Korean leader Kim Jong Un provides guidance with Ri Hong Sop (2nd L) and Hong Sung Mu (R) on a nuclear weapons program in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang KCNA via REUTERS