Want to know more about what we know about Wednesday's test - such as that if it was a full thermonuclear device, it should have generated a seismic measurement of "around seven on the earthquake scale"? 

We spoke to nuclear and defence experts to bring you this comprehensive guide.

North Korea's test was carried out underground - but that didn't leave many options for new broadcasters seeking images to illustrate their news reports. This South Korean broadcaster went for familiar mushroom-cloud footage from previous explosions - though there would have been no such cloud created in Wednesday's test.

Image source, AFP

Many commentators have lamented the fact that the world has few diplomatic options against North Korea, which is already under extensive sanctions.

One North Korea scholar is pessimistic about the prospects, external that North Korea will relinquish its weapons programme. 

Seismologist @stevenjgibbons, external says the test signals were recorded as far away as Norway:

North Koreans often cite the threat they say is posed by the nuclear-armed United States. Until 1991 the US did deploy nuclear weapons on the Korean peninsula, say historians, but they were withdrawn under President George Bush senior.

Nato Secretary-General Jens Stoltenberg has urged Pyongyang to "abandon nuclear weapons and existing nuclear and ballistic missile programmes in a complete, verifiable and irreversible manner and engage in credible and authentic talks on denuclearisation".

Randy Bell, director of the Comprehensive Test Ban Treaty Organization International Data Centre in Vienna, says automatic processing has "showed results very consistent with the 2013 nuclear test", which was not an H-bomb.

"The location was very similar. The characteristic of the wave forms were very similar.”

"Human review is now under way of all these signals," Mr Bell adds, with results ready in 48 hours. 

It bears repeating that North Korea's claims to have tested a hydrogen bomb - much more complex to develop than an atomic bomb - are being viewed with considerable scepticism. Experts say the resulting explosion should have been far more powerful than it was. Even China, which is closest to North Korea among world powers, is advocating caution.

We've just posted up some video of North Koreans dutifully cheering the news of the alleged H-bomb test. "I think it is very obvious to counter a robber waving a nuclear stick with a nuclear stick," points out one spectator.

@stanyee has found a bluntly named road near at site of the latest test on Google Maps.

@mpspavor has posted this interesting North Korean artwork. The text reportedly translates as "Let’s work towards future generations not knowing" - in other words, let's work towards a nuclear-free world where future generations don't even know what nuclear weapons are. Clearly we aren't there yet. 

This episode has reminded some more satirical commentators of a song that did the rounds in the era of the Cold War, a verse of which ran:

"Then raise the workers’ bomb on high,

Beneath its cloud we’ll gladly die,

For though it sends us all to hell,

It kills the ruling class as well. " 

So, to sum up the reaction of key powers to North Korea's nuclear test so far: 

• China, Pyongyang's most powerful ally, said it "firmly opposed" the test
• South Korea's President, Park Geun-Hye, described it as a "grave provocation" and a threat to South Korea's future 
• Russia's foreign ministry described it as a "severe violation of international law" 
• In the United States, the White House said it would respond appropriately to any provocation. 
• Japan's Prime Minister Shinzo Abe described it as a serious threat to his country's safety 

The UN Security Council will meet later to discuss the issue.

The human costs of the conflict and 70-year division of the Korean peninsula are visible on the south side of the DMZ which separates the two sides at the 38th parallel. Here, ribbons bearing messages and prayers for peace, reunification and lost family members flutter below the barbed wire.

Image source, Getty Images

Japan's Prime Minister Shinzo Abe is shown here emphatically responding to the North Korean test in parliament. "We absolutely cannot allow this," he said.

Image source, AFP

More from that Russian statement, which went on to call for talks to restart.

"We reiterate our position in favour of a diplomatic solution to the problems of the Korean Peninsula within the framework of the six-party talks and the earliest possible start of a dialogue aimed at forming a reliable system of peace and security in the region."

The talks - between N Korea, S Korea, the US, Russia, Japan and China - have stopped and started for years, and were last abandoned in 2009.

The EU adds its words of censure.

"If confirmed, this action would represent a grave violation of [North Korea's] international obligations not to produce or test nuclear weapons, as determined by several United Nations Security Council Resolutions," foreign policy chief Federica Mogherini said in a statement. She said it would also be "a threat to the peace and security of the entire Northeast Asia region", reported Reuters news agency.

Russia has joined the chorus of those condemning the test. 

If confirmed, it would amount to "a severe violation of international law and UN Security Council resolutions", the Russian Foreign Ministry says in a statement, external (in Russian). "Such actions can exacerbate the situation on the Korean peninsula, which has a high potential for military-political confrontation."

This image from the North Korean capital, Pyongyang, shows well-to-do citizens apparently celebrating the leadership's claim that it has successfully carried out an H-bomb test.

Image source, AP

This map details North Korea's test sites over the years, and the magnitude of the explosions generated