North Korea’s increasingly dangerous dictator Kim Jong-un has “slapped China in the face” by detonating what is believed to be a nuclear device, risking harsh sanctions from the international community.

During a broadcast from North Korean state news agency KCNA on Wednesday, the communist nation claimed to have tested a hydrogen bomb (many times more powerful than an atomic bomb) in an underground site in its north-west.

The broadcast described the weapon as the “H-bomb of Justice” built to defend against “chieftain of aggression” the United States and its “gang of cruel robbers”, the world.

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China is one of the few nations with which the reclusive dictatorship has regular contact. Experts told The New Daily the detonation would further strain Beijing-Pyongyang relations.

“They have been trying to regain the special relationship they previously had,” Sydney University international security expert Andrew Kwon said.

“For Beijing it would be considered a slap in the face to China and also a possibility that they’ve failed to bring North Korea back into line.”

The Chinese government joined the global community in denouncing the test, saying it was “firmly opposed” to the action, of which it denied having any forewarning.

“We strongly urge the DPRK to honour its commitment to denuclearisation, and to cease any action that may deteriorate the situation,” China’s foreign ministry said in a statement.

Australian foreign minister Julie Bishop said she believed China was as “frustrated” as the rest of the international community with North Korea, giving her hope that Beijing would back sanctions against the regime.

“We will continue to work with partners and allies, and the rest of the international community to place pressure on North Korea so it stops this provocative behaviour,” Ms Bishop told the Nine Network on Thursday.

Doubts cast over veracity of ‘hydrogen bomb’ claims

American, South Korean and Chinese officials were still trying to independently verify whether the magnitude-5.1 tremor registered near Punggye-ri nuclear testing facility at 12:30pm AEDT was a hydrogen bomb.

However, nuclear experts speaking to the ABC cast doubt on North Korea’s claims, saying the detected seismic activity suggested a less powerful device.

North Korea released this photo of Jong-un purportedly signing off on the testing.

Crispin Rovere, an Australia-based nuclear policy and arms control specialist, said the 5.1 magnitude tremor detected at the North’s Punggye-ri nuclear test site was too small to support Pyongyang’s claim.

“The seismic data that’s been received indicates that the explosion is probably significantly below what one would expect from an H-bomb test,” Mr Rovere said.

The test came just two days before Mr Kim’s birthday. Analysts said the North’s leader had been looking for a major achievement to highlight at a rare ruling party congress scheduled for May, the first gathering of its kind for 35 years.

“I don’t think it was a hydrogen bomb test — the explosion had to be larger if it was a hydrogen bomb test,” said Choi Kang, vice president of the Seoul-based Asan Institute for Policy Studies.

Fears for Kim Jong-un’s ruthlessness

University of Adelaide North Korea expert Professor Felix Patrikeeff told The New Daily that the development was alarming because of the highly “autocratic” and “wilful” leadership of Kim Jong-un.

Professor Patrikeeff said the H-bomb’s testing could prove Jong-un a more volatile leader than his father and grandfather – former supreme leaders Kim Jong-il and Kim Il-sung.

The newsreader said DPRK was a “responsible nuclear state”.

“The North Korean leadership has been in a fair amount of real turmoil with Kim Jong-un behaving in a very wilful fashion,” Professor Patrikeeff said.

“He is being a greater and greater autocratic character so it is also a question of how mature is his thinking?

“Has he matured to the point where he knows how to play the game in the same way that his father did? Or is he likely to act as a greater maverick than his father and, if so, can he play the game of double bluff to not enter some potentially difficult waters?”

He said North Korea could not “be counted on to act in a rational fashion” and that its development brought the nation into a “new realm” of nuclear weaponry.

Currently only Russia, the US, the United Kingdom, France and China have hydrogen bombs in their nuclear arsenals.

“This makes it all the more worrying becuase up until now it has been states that are quite politically stable and responsible having these bombs,” he said. 

“With North Korea apparently joining that group it takes the world to a new level of difficulty.”

World slams ‘grave breach of UN resolutions’

South Korean President Park Geun-hye wants the world to come down hard on Pyongyang. Photo: AAP

Before China had officially commented on the test, its state-run news agency published an editorial condemning the North Korea’s actions.

“It is not good for anyone for there not to be peace on the Korean Peninsula. Any act that disrupts stability in north-eastern Asia is undesirable and unwise,” it said.

The White House could not confirm the test, but in a statement said: “[The US] will not accept [North Korea] as a nuclear state”.

Russia also denounced the tests.

“Such actions are fraught with further aggravation of the situation on the Korean peninsula, which is anyway marked by very high potential of military and political confrontation,” Russia foreign ministry’s spokeswoman, Maria Zakharova said.

Australia’s foreign minister Julie Bishop called on international bodies, including the United Nations Security Council, to provide a strong response to North Korea’s actions.

South Korean President Park Geun-hye said the country will take decisive measures against any additional provocations by the North, and would make sure the isolated country pays the price for its latest nuclear test.

– with ABC