China is unlikely to take strong action in response to North Korea's claimed test of a hydrogen bomb, according to experts who say Beijing prefers the devil it knows to the uncertainty that could follow a confrontation.
And whether Pyongyang would even listen is highly questionable, they say.
Governments around the world have long pushed the Asian giant to moderate its wayward neighbour's bad behaviour, arguing that Beijing's support for Pyongyang gives it particular influence over the hermit kingdom.
But that is ever less true, experts say. Relations forged in the blood of the Korean War -- with the countries once called "as close as teeth and lips" -- have taken a licking since Kim Jong-Un took control of North Korea following the 2011 death of his father.
"China's influence on North Korea is becoming weaker and weaker, the main issue is that the North's leadership do not listen, they are very stubborn", said Zhu Feng, an expert on international relations.
Pyongyang, he added, may believe it can "exploit" its relationship with its main diplomatic protector while Beijing is distracted by tensions with other neighbours and the US in the South China Sea.
Beijing -- which regularly calls for calm on the Korean peninsula -- has become increasingly frustrated with its neighbour's antics, a feeling undoubtedly exacerbated by its fourth nuclear test.
Unlike his father Kim Jong-Il, Pyongyang's current leader has not visited Beijing since coming to power.
Last month, he dispatched his all-girl pop group, the Moranbong band, to serenade China's top leaders in what was widely seen as a sign of warming ties, potentially heralding a trip.
But while they were in Beijing, Pyongyang announced it had developed an H-bomb and the band suddenly headed home on the eve of their performance, leaving relations in the deep freeze.
Only four days later Kim signed the order to begin 2016 with the "thrilling sound of the first hydrogen bomb explosion."
- 'Risky, irresponsible, reckless' -
Despite the shock developments, Zhu said, China's foreign ministry stuck to familiar language, firmly opposing the nuclear test and -- yet again -- calling for the resumption of the moribund six-party talks.
Commentaries in state-run media Thursday were also true to form, scolding the country but falling short of a call for direct action from Beijing.
An editorial in the government-published China Daily described the test as "risky, irresponsible and reckless", but said the problem was best addressed through the "collective wisdom and determination" of the international community.
There was no mention of what, if any, steps Beijing could or should pursue on its own.
In any case, Pyongyang is unlikely to prove receptive to Chinese measures.
"Kim Jong-Un might feel that he has, you know, sort of a nothing to lose kind of mentality", said Wang Dong, an associate professor at Peking University's School of International Studies.
If so, that leaves the international community in a "very difficult situation", he said. "How are you going to deal with a guy who feels, who believes, that he has nothing to lose?"
- Keeping the regime afloat -
The test, two days before Kim's birthday, was a striking act of defiance in the face of warnings that Pyongyang would pay a steep price if it continued pursuing its atomic weapons programme.
The three previous tests in 2006, 2009 and 2013 triggered waves of UN sanctions, largely focused on individuals and companies linked to the weapons programme.
But China, a permanent member of the Security Council, argues that dialogue is the only way to moderate its behaviour and remains a major exporter to North Korea.
According to figures from China Customs, the country exported more than 176,000 tonnes of refined oil to North Korea in the first 11 months of 2015 -- more than the total for 2014 -- and over 23 million tonnes of grain.
But underlying everything is Beijing's desire to keep North Korea as a buffer between it and the prospect of US troops stationed on its border in a unified Korea.
"China keeps the Kim regime afloat with fuel supply, food assistance and an opening out of diplomatic and economic isolation," said Yanmei Xie, a senior analyst at the International Crisis Group.
"For explosion."
- 'Risky, irresponsible, reckless' -
Despite the shock developments, Zhu said, China's foreign ministry stuck to familiar language, firmly opposing the nuclear test and -- yet again -- calling for the resumption of the moribund six-party talks.
Commentaries in state-run media Thursday were also true to form, scolding the country but falling short of a call for direct action from Beijing.
An editorial in the government-published China Daily described the test as "risky, irresponsible and reckless", but said the problem was best addressed through the "collective wisdom and determination" of the international community.
There was no mention of what, if any, steps Beijing could or should pursue on its own.
In any case, Pyongyang is unlikely to prove receptive to Chinese measures.
"Kim Jong-Un might feel that he has, you know, sort of a nothing to lose kind of mentality", said Wang Dong, an associate professor at Peking University's School of International Studies.
If so, that leaves the international community in a "very difficult situation", he said. "How are you going to deal with a guy who feels, who believes, that he has nothing to lose?"
- Keeping the regime afloat -
The test, two days before Kim's birthday, was a striking act of defiance in the face of warnings that Pyongyang would pay a steep price if it continued pursuing its atomic weapons programme.
The three previous tests in 2006, 2009 and 2013 triggered waves of UN sanctions, largely focused on individuals and companies linked to the weapons programme.
But China, a permanent member of the Security Council, argues that dialogue is the only way to moderate its behaviour and remains a major exporter to North Korea.
According to figures from China Customs, the country exported more than 176,000 tonnes of refined oil to North Korea in the first 11 months of 2015 -- more than the total for 2014 -- and over 23 million tonnes of grain.
But underlying everything is Beijing's desire to keep North Korea as a buffer between it and the prospect of US troops stationed on its border in a unified Korea.
"China keeps the Kim regime afloat with fuel supply, food assistance and an opening out of diplomatic and economic isolation," said Yanmei Xie, a senior analyst at the International Crisis Group.
"For explosion."
- 'Risky, irresponsible, reckless' -
Despite the shock developments, Zhu said, China's foreign ministry stuck to familiar language, firmly opposing the nuclear test and -- yet again -- calling for the resumption of the moribund six-party talks.
Commentaries in state-run media Thursday were also true to form, scolding the country but falling short of a call for direct action from Beijing.
An editorial in the government-published China Daily described the test as "risky, irresponsible and reckless", but said the problem was best addressed through the "collective wisdom and determination" of the international community.
There was no mention of what, if any, steps Beijing could or should pursue on its own.
In any case, Pyongyang is unlikely to prove receptive to Chinese measures.
"Kim Jong-Un might feel that he has, you know, sort of a nothing to lose kind of mentality", said Wang Dong, an associate professor at Peking University's School of International Studies.
If so, that leaves the international community in a "very difficult situation", he said. "How are you going to deal with a guy who feels, who believes, that he has nothing to lose?"
- Keeping the regime afloat -
The test, two days before Kim's birthday, was a striking act of defiance in the face of warnings that Pyongyang would pay a steep price if it continued pursuing its atomic weapons programme.
The three previous tests in 2006, 2009 and 2013 triggered waves of UN sanctions, largely focused on individuals and companies linked to the weapons programme.
But China, a permanent member of the Security Council, argues that dialogue is the only way to moderate its behaviour and remains a major exporter to North Korea.
According to figures from China Customs, the country exported more than 176,000 tonnes of refined oil to North Korea in the first 11 months of 2015 -- more than the total for 2014 -- and over 23 million tonnes of grain.
But underlying everything is Beijing's desire to keep North Korea as a buffer between it and the prospect of US troops stationed on its border in a unified Korea.
"China keeps the Kim regime afloat with fuel supply, food assistance and an opening out of diplomatic and economic isolation," said Yanmei Xie, a senior analyst at the International Crisis Group.
"For Beijing, a nuclear armed North Korea is uncomfortable and disturbing", she said.
"But a regime collapse in Pyongyang leading to mass chaos next door and potentially a united Korean peninsula with Washington extending its influence northward to China's doorstep is downright frightening."
Media captionThe bomb test was announced on North Korean state television
North Korea says it has successfully tested a hydrogen bomb amid reports of a tremor near the main nuclear test site.
State media announced the test after monitors detected a 5.1 magnitude quake close to the Punggye-ri site.
The North is thought to have conducted three previous underground nuclear tests there since 2006.
A hydrogen bomb uses fusion to create a blast far more powerful than that of a more basic atomic bomb. Follow our live coverage here
Analysis: Stephen Evans, BBC Korea correspondent
Image copyrightReutersImage caption North Korean leader Kim Jong-un was shown attending an apparent submarine missile test last year This test was apparently a hydrogen bomb, a step up in destructive power from the plutonium used in previous tests. It gives more explosive power for a lighter weight.
After the test in 2013, there was widespread condemnation. The UN Security Council held an emergency meeting at which its members, including China, "strongly condemned" the test. Similar outrage is expected this time. Prime Minister Abe of Japan has said this fourth test was a "serious threat to the safety of his nation".
On top of any fourth nuclear test, North Korea also appears to have tested a submarine-launched missile. The ability to launch missiles from submarines would change the whole calculation of military response because warning times of an attack on, for example, the West Coast of the United States would be much shorter.
Before the test, North Korean state media said the country "deserved to hold nuclear weapons... to counter nuclear threats by the US".
Experts believed before the fourth test that North Korea was still some years from being able to hit a target with a nuclear bomb delivered by a missile. But it is crystal clear that it is absolutely determined to be able to do so. It is also clear that it is improving its abilities rapidly. How advanced is North Korea's nuclear programme? North Korea's nuclear tests
If confirmed, it would mean Pyongyang is intent on pursuing its nuclear programme with little regard for the major political and diplomatic costs that will inevitably accompany this unwelcome development, says Dr John Nilsson-Wright of Asia Programme at Chatham House.
In a surprise announcement a newsreader on North Korean state TV said: "The republic's first hydrogen bomb test has been successfully performed at 10:00 am on January 6, 2016."
Last month, North Korean leader Kim Jong-un said Pyongyang had developed a hydrogen bomb, although international experts were sceptical.
What is a hydrogen bomb?
A weapon energised by the nuclear fusion of hydrogen isotopes in a chain reaction, developed in 1958 by the United States
Also known as a thermo-nuclear bomb, it is seen as a "cleaner" bomb than an atomic one as it has less radioactive fallout - but also much more powerful
Unlike an atomic bomb, powered by nuclear fission, a hydrogen bomb is powered by the fusion of lighter elements into heavier elements
Such bombs can be as small as a few feet long and can fit in warheads of ballistic missiles
Suspicion of a test was first raised after the US Geological Survey said the epicentre of the quake - detected at 10:00 Pyongyang time (01:30 GMT) was in the north-east of the country, some 50km (30 miles) from Kilju city, near Punggye-ri.
Hours before the seismic activity, South Korean media reported that Pyongyang had test-fired a ballistic missile from a submarine in late December. It is unclear whether the test was successful or not.
In May last year, North Korea claimed it had successfully launched a missile from a submarine. Strong reaction started pouring after the North Korean announcement of the hydrogen bomb test with South Korea saying it was a serious challenge to global peace and a violation of UN Security Council resolutions.
The Japanese Prime Minister Shinzo Abe said it was a threat to Japan's safety and could not be tolerated.
The US called on North Korea to abide by its international commitments and obligations saying it would respond to provocations.
After previous tests, the international community has responded with economic and political sanctions.
North Korea and nuclear weapons
Image copyrightGeoEyeOctober 2002: North Korea first acknowledges it has a secret nuclear weapons programme October 2006: The first of three underground nuclear explosions is announced, at a test site called Punggye-ri May 2009: A month after walking out of international talks on its nuclear programme, North Korea carries out its second underground nuclear test February 2013: A third nuclear test takes place using what state media calls a "miniaturised and lighter nuclear device" May 2015: Pyongyang claims to have tested a submarine-launched missile, which are more difficult to detect than conventional devices January 2016: North Korea says it has successfully tested a hydrogen bomb
