President Trump has also criticised both China and South Korea for their approaches towards the "rogue nation".

North Korea has become a "great threat and embarrassment to China", its ally, which had had "little success" in finding a solution he said.

Meanwhile, South Korea's "talk of appeasement" towards North Korea "will not work", Mr Trump said.

US President Donald Trump has reacted to North Korea's "major nuclear test".

The country's "words and actions continue to be very dangerous to the United States..." he says.

People in the North Korean capital Pyongyang have been learning of their nation's latest step down its atomic weapons path, and these individuals were pictured reacting in celebratory fashion.

Image source, AFP

Image source, AFP

Image source, AFP

Image source, AFP

BBC Monitoring
The world through its media

South Korean experts and government agencies have made differing assessments on the potency of what North Korea claims was a successful hydrogen bomb test.

• South Korea's weather agency, the Korea Meteorological Administration, notes that the explosive yield of the latest test was five to six times higher than that of North Korea's previous nuclear explosion conducted a year ago, The Korea Times reports., external
• The Korea Herald says, external Kim Young-woo, a South Korean lawmaker who also chairs the National Assembly National Defence Committee, believes the explosion was "more powerful than the nuclear bomb detonated in Japan's Nagasaki. Four or five times more powerful".
• Kim Dong-yub, a professor at the Institute for Far Eastern Studies at Kyungnam University, put it at 60-80 kitotons,, external short of some 100kt caused by a "real H-bomb".
• Park Jung-jin,, external a researcher at the Institute for Far Eastern Studies, says: "It seems that the North has made it clear once again that it wants to be recognised as a nuclear-armed state. It is more likely to double down on its push for advancing its nuclear weapons program."

North Korea's nuclear programme has been a source of great concern for more than 20 years.

Image source, Google

People in Yanbian, the Chinese region next to north-eastern North Korea, have been reacting to the nuclear test today on social media.

On the most popular site, microblogging platform Sina Weibo, many say they felt the quake strongly, which is "scary".

Some want to know if such tests have any impact on the environment, with some wondering if they might trigger a volcanic eruption inside Changbai mountain.

Others complained that the Chinese government doesn't care about them as they don't seem to be taking strong action against North Korea.

Away from Yanbian, some Chinese commenters have mockingly described the Chinese foreign ministry as a "copy and paste machine" as they hear the same statements from the ministry time after time.

AFP

French President Emmanuel Macron has called for a "very firm" response by the international community to North Korea's announcement that it had successfully tested a nuclear bomb.

"The international community must be very firm in its handling of this latest provocation," he said in a statement, calling on the UN Security Council to "quickly react" to the escalation.

Image source, EPA/USGS

North Korea has hailed its sixth "perfect success" of a nuclear test. The seismic readings indicate it is bigger than any other it has conducted, but the apparent collapse of a tunnel at the test site could provide valuable information, nuclear defence analyst Catherine Dill writes.

Why would the tunnel collapse? It could be that the tunnel was not constructed sufficiently to handle an explosion of that size. It's also possible that they intended for this collapse to occur - a way of signalling to the world that this was an authentic test through radionuclide release, a serious advance. It is still too early to tell.

What it does mean is that we are likely to get information to analyse this nuclear explosion to determine what happened under the mountains of the test site. This will take weeks or even months as monitoring sites run by the CTBTO detect these radionuclides.

The information they give us may tell us the composition of the warhead: how much fissile material there was and what kind - was it plutonium or highly enriched uranium?

Read more from Catherine

Robin Brant
China Correspondent

China's state-run Global Times newspaper has been reacting to the nuclear test.

It has been suggested that the second recorded seismic event was a collapse in the tunnel where the device was tested.

Defence expert Melissa Hanham is among those on Twitter who spotted a rather startled reaction to North Korea's latest bomb test, from someone who works in that field.

Some observers are saying the timing of the test - which took place shortly before Chinese President Xi Jinping opened the BRICS summit in Shanghai - could not have been a coincidence.

"Nicely done" and "What nerve" are some of the comments this upstaging of the Chinese leader by his younger North Korean counterpart has elicited.

That Kim Jong-un feels able to do this to its ally is noteworthy.

China is simply in the wrong place on North Korea, the BBC's China Editor Carrie Gracie says. It is allowing Kim Jong-un's nuclear ambitions to undermine Chinese national interest, she adds.

There are complex reasons for this including history, habit and political culture. But among Chinese foreign policy experts and even on social media, unease is beginning to spread.

China seems trapped in an unfinished history marked by binary choice: a nuclear-armed North Korea or a reunified Korea with American troops on China's border. Between these choices, it finds a nuclear-armed North Korea preferable.

Read more from Carrie:

Why Beijing should lead on the North Korean crisis

Robin says there's no sign, though, that China is willing yet to see that "firm will" go beyond UN sanctions which recently clamped down on seafood and iron ore exports, in addition to the coal and minerals that are already banned from crossing the border.

"It's noteworthy that this test took place just as China's president was about to welcome a handful of world leaders to a two-day showpiece summit here on the east coast. Set piece international events like this are important to China. But even the state-controlled media will find it hard to ignore the fact that their man has been upstaged - embarrassed too - by its almost universally ostracised ally and neighbour."

The BBC's China Correspondent Robin Brant says North Korea's nuclear test is a slap in the face to its ally China.

"Rebukes don't come much stronger than this. North Korea's sixth nuclear weapons test is an utter rejection of all that its only ally has called for. Beijing's response was predictable: condemnation, urging an end to provocation and dialogue. But it also spoke of urging North Korea to 'face up to the firm will' of the international community to see denuclearisation on the Korean Peninsula."

South Korea's Foreign Minister Kang Kyung-wha spoke with her Japanese counterpart Taro Kono on the telephone to discuss countermeasures against North Korea's latest nuclear test, according to a foreign ministry official in Seoul.

South Korea's President Moon Jae-in has branded the North Korean nuclear test an "absurd" mistake.

He called for the "strongest response" and said new UN Security Council resolutions should be adopted to completely isolate Pyongyang.

Image source, AFP/Getty

Japan's NHK says PM Shinzo Abe and President Donald Trump have spoken on the phone for about 20 minutes. They agreed to work with South Korea to increase pressure on North Korea, it said.

NHK said Mr Abe, external wants to "calmly analyse a range of information he is receiving, discuss necessary action with other countries, and take all possible measures to protect people's lives and assets".

Image source, Reuters

The Korea Times has been speaking to people across South Korea to see how worried they are. The general mood seems to be that there's nothing much new about North Korean belligerence and provocation.

"Kim Jong-un will not use the bomb since that means he will die," says one woman in Seoul., external

"It's been worse before but still did not lead to war," says Yoon Tae-jun, 29, from Busan, before adding: "But then again I'm not sure this time because of Trump."

Image source, EPA