North Korea says it has conducted a "successful" hydrogen bomb test, which is believed to have caused a massive tremor that prompted evacuations as far away as China.

Key points: North Korea claims to have successfully carried out its first hydrogen bomb test

North Korea claims to have successfully carried out its first hydrogen bomb test Magnitude-5.1 tremor at surface depth registered near Punggye-ri nuclear testing facility at 12:30pm AEDT

Magnitude-5.1 tremor at surface depth registered near Punggye-ri nuclear testing facility at 12:30pm AEDT The North has previously conducted tests in 2006, 2009 and 2013 at location of latest tremor

South Korea, US and Chinese authorities have scrambled for confirmation of the test, however officials in Seoul have cast doubt on the claim it was a hydrogen bomb saying no radiation had been detected.

If confirmed, the explosion marks a major step forward in the country's nuclear development.

The surprise test was personally ordered by North Korean leader Kim Jong-un and came just two days before his birthday.

"Let the world look up to the strong, self-reliant nuclear-armed state," Mr Kim wrote in what North Korean state television displayed as a handwritten note.

"The republic's first hydrogen bomb test has been successfully performed ... based on the strategic determination of the Workers' Party," a news reader announced on Wednesday.

North Korean leader Kim Jong-un has previously held bomb tests at the site in the country's north-east. ( AFP: Korean Central News Agency )

"With the perfect success of our historic H-bomb, we have joined the rank of advanced nuclear states.

"The latest test, completely based on our technology and our manpower, confirmed that our newly-developed technological resources are accurate and scientifically demonstrated the impact of our miniaturised H-bomb."

A magnitude-5.1 tremor was earlier detected by the US Geological Survey (USGS) and South Korean officials said they suspected it was an explosion.

H-bomb or A-bomb? Sorry, this video has expired Hydrogen bomb explained Simply put, atomic bombs' nuclear fission is the process of splitting atomic nuclei, while hydrogen bombs' fusion is joining them

Simply put, atomic bombs' nuclear fission is the process of splitting atomic nuclei, while hydrogen bombs' fusion is joining them In H-bombs, TNT ignites an A-bomb to detonate adjacent to a fusion fuel such as tritium, deuterium or lithium deuteride, compressing them at extreme pressures and at a very rapid rate to start a fusion reaction

In H-bombs, TNT ignites an A-bomb to detonate adjacent to a fusion fuel such as tritium, deuterium or lithium deuteride, compressing them at extreme pressures and at a very rapid rate to start a fusion reaction Nuclear fusion is the process that occurs in the heart of the sun, and requires immense temperatures to ignite

Nuclear fusion is the process that occurs in the heart of the sun, and requires immense temperatures to ignite H-bombs, thermonuclear bombs and fusion bombs can be thousands of times more powerful than atomic bombs, atom bombs, A-bombs, or fission bombs Source: ABC/AFP

"We suspect a man-made earthquake, and are analysing the scale and epicentre of the quake with the geoscience and mineral resource institute of South Korea," a Korea Meteorological Administration (KMA) official said.

A revised location of the tremor by the USGS put it at the same location as previous tests in 2006, 2009 and 2013, and at surface depth.

Chinese border residents, however, were evacuated from buildings after feeling the tremors, state broadcaster China Central Television (CCTV) said on a verified social media account.

The areas included Yanji, Hunchun and Changbai in Jilin province, some of the counties closest to the North's nuclear test site.

Students at a senior high school were dismissed during an examination after its recreation ground cracked, it added.

Last month, Mr Kim suggested Pyongyang had already developed a hydrogen bomb, although the claim was greeted with scepticism by international experts.

The North's miniaturisation claims have also not been independently verified.

A hydrogen, or thermonuclear, device uses fusion in a chain reaction that results in a powerful explosion.

Unexpected test draws immediate condemnation

The nuclear test drew condemnation abroad, with China, the North's chief ally, expressing "resolute opposition" and saying it would lodge a protest with Pyongyang.

The United Nations Security Council is planning to hold an emergency meeting on Wednesday (New York time) to discuss the test, three council diplomats have said.

It was not immediately clear what action, if any, the 15-nation council was planning to take in response to the statement.

Analysis: North Asia correspondent Matthew Carney in Beijing The last bomb, in 2013, was about magnitude 4.9 on the Richter scale. This time, it was only 5.1. Experts have said if this really was a true H-bomb, then you could expect up to 10 times this on the Richter scale, which obviously leads us to two conclusions. One, the regime is actually lying about it. A couple of weeks ago, we had North Korea's leaders saying that they would do it and that they did have the capacity, so maybe he is carrying on that threat. Or secondly and probably more likely, it was perhaps a failure to ignite this H-bomb and start this two-stage thermonuclear process. What they are trying to do is miniaturise the technology, to put the device on top of their inter-continental ballistic missiles, to hit the coast of America. This is the fourth test and in 10 years, they're really just still at the stage of a Hiroshima-style bomb that America dropped in Japan.

Foreign Minister Julie Bishop has called on international bodies, including the council, to provide a strong response to North Korea's actions.

"[The] nuclear test confirms North Korea's status as a rogue state and a continuing threat to international peace and security," Ms Bishop's statement said.

While vowing to stick by a no-first-use policy, North Korea said it would continue to pursue an advanced nuclear strike capability.

"As long as the vicious anti-North policy of the US persists, we will never stop development of our nuclear program," its state television news reader said.

The White House said it could not confirm the claims of miniaturisation and a hydrogen bomb test, but added the United States would respond appropriately to provocations and defend its allies.

Prime Minister Shinzo Abe said Japan would make a firm response to North Korea's challenge against nuclear non-proliferation.

"North Korea's nuclear test is a serious threat to our nation's security and we absolutely cannot tolerate it," Mr Abe told reporters.

"We strongly denounce it."

South Korea's intelligence agency said the device may not have been a hydrogen nuclear bomb, Yonhap news agency reported.

Its meteorological agency said separately that it had not detected any radiation.

The Punggye-ri nuclear test facility in Sungjibaegam was used by the country to detonate tests between 2006 and 2013. ( AFP: Geoeye )

In Seoul, the presidential Blue House called an emergency meeting of the National Security Council as officials scrambled to confirm the precise nature of the tremor.

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

China's Xinhua state news agency said a new test runs counter to the goal of denuclearisation, and warned that any practice that disrupts stability in northeast Asia is "undesirable and unwise".

A nuclear test is as a major slap in the face to its chief ally China, and extinguishes any chance of a resumption of six-country talks on North Korea's nuclear program that Beijing has been pushing for.

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