"Nothing is more foolish than dropping a hunting gun before herds of ferocious wolves." In a statement released shortly after its nuclear test, North Korea said it needed nuclear weapons to defend itself from aggressors such as the US, which it called "a gang of cruel robbers". Full statement here, external. 

 More from the press briefing at China's foreign ministry.   

The Chinese government is "strongly opposed" to North Korea's nuclear test, "It's China's stance to promote the denuclearization of Korea Peninsula, prevent nuclear proliferation and maintain peace and stability in Northeast Asia. We strong urge North Korea to abide by her pledges and stop taking any actions that might make the situation worse".

The impact of the underground explosion can be seen in this chart at Taiwan's Seismology Center

Image source, AFP

A former British ambassador in Pyongyang, John Everard, says the North Koreans have "a deep sense of victimhood" and he believes this is a bad sign from the regime.

 "Anything that produces a seismic shock of 5.1 is dangerous," he told the BBC. "In the end, whether they did this by nuclear fission or by a hydrogen bomb is of concern. But an explosion of that size is quite enough to wipe out a city and I think that, of course, is deeply worrying."

No radiation has so far been detected from the nuclear test at Japanese monitoring posts, Japan's top government spokesman Yoshihide Suga said, according to Reuters news agency

More reactions from South Korea and China: "There is an extremely big gap between this and the usual strength of hydrogen bombs... the data doesn't support suggestions that the bomb was a hydrogen bomb," says military expert Du Wenlong on state broadcaster CCTV, external."The problem is that the international community has no other viable option but to slap additional sanctions against the regime in Pyongyang despite doubts about the efficacy of such measures" and Seoul must be "much bolder about finding ways to make a breakthrough in the stalled inter-Korean relationship", says this editorial in The Korea Times, external.

The BBC's Korea Correspondent, Stephen Evans, says that though there has been international condemnation, there appears to be not much leverage on North Korea, as it already experiences very tight sanctions with virtually no trade with the outside world.Though China has some leverage, it also does not want the regime to collapse chaotically with the prospect of US or South Korean troops coming in to fill that vacuum, says our correspondent.

Cartoons about North Korea are proving popular with many Twitter users. This one of leader Kim Jong-un was drawn and shared by artist Mark Winter. 

The US is just one of several countries to criticise North Korea's latest nuclear test. Read their responses in our latest story.

The US embassy in Seoul has shared a statement on North Korea's latest nuclear ambitions on its Twitter page.

"While we cannot confirm these claims at this time, we condemn any violation of UN Security Council Resolutions and again call on North Korea to abide by its international obligations and commitments," it says.

Despite its close relationship with North Korea, China says it was caught off-guard by the nuclear test.

In a tweet by state newspaper, the People's Daily, China's foreign ministry has announced that emergency radiation tests will be carried out in border areas to determine the impact of North Korea's apparent hydrogen bomb test.

Jasper Kim of the Asia-Pacific Global Research Group tells the BBC that North Korea and China have "less of a little brother-big brother relationship now" with North Korea becoming "more boisterous, independent and less predictable" in recent years. China has condemned the latest nuclear test, as it has done for previous ones.

South Korea's Yonhap news agency has tweeted the following:

North Korea's latest nuclear announcement is still one of the biggest trending topics, external on China's popular microblogging site Weibo, which is seeing thousands of Chinese netizens actively responding to the news. Some Chinese social media users have expressed concern about Pyongyang's hydrogen bomb claims. "This is disturbing news - if genuinely true. Will North Korea bring about World War Three? I hope China takes an even tougher stand against such a volatile neighbour" said a Weibo user in Beijing."This was such horrible news to wake up to," said another user. "Whether or not we should take North Korea seriously is another matter. The country is still dangerous."Other users on the site however, remained unconvinced by the news. "Empty threats. Another cheap attempt by their failed government to scare the world into thinking they are something to be reckoned with," said Weibo user Huang Yu Jing. Another remarked: "Try harder, Kim. The rest of the world isn't fooled by your tricks."

Image source, Weibo

British Foreign Secretary Philip Hammond has been commenting on the development while on a visit to Beijing, saying "if a nuclear device has been detonated by North Korea, this is a grave breach of UN Security Council resolutions and a provocation which I condemn without reservation. 

"It underlines the very real threat that North Korea represents to regional and international security."

Image source, Reuters

Russian media has been sceptical about the latest claims.

"There is still doubt whether North Korea is technically capable of creating its own nuclear weapons," state-run Rossiya 24 TV reported."This may be yet another bluff aimed at getting more humanitarian aid and food for the people of North Korea," NTV asked.

Phil Robertson of Human Rights Watch says in a statement, external: "The only birthday present that Kim Jong-un should get from the international community is a one-way trip to the International Criminal Court in The Hague, where he should be put on trial for crimes against humanity." Kim Jong-un's birthday is 8 January.