What is this really all about?
Test or otherwise, North Korea's announcement was aimed at sending a message to both domestic and international audiences.
Kim Jong Un, who is believed to be aged in his early 30s, wants to cement his status at home as a leader while simultaneously showing the outside world that Pyongyang is a force to be reckoned with, according to analysts.
"The dynasty which runs North Korea is a dictatorship — it's dysfunctional in all sorts of ways — but it has its own rationale which is to display its invulnerability to outside pressure or aggression," said Francois Heisbourg, a special adviser at the Paris-based Foundation for Strategic Research. "This is a show of strength."
Does this change the game?
North Korea isn't yet a nuclear behemoth, but has been working hard to become one.
The country is believed to have a handful of nuclear warheads and has carried out three previous nuclear tests since 2006 — for which it earned United Nations sanctions.
That doesn't mean North Korea is all the way there though: Pyongyang lacks the missile technology to launch those weapons long distances, according to Western officials and experts.
"It doesn't have a nuclear arsenal — it has the ability for the time being to produce nuclear devices which it knows how to detonate," Heisbourg said. "It is not yet clear that it has the ability to operationalize these devices so that it can be put on top of a rocket and shot at somebody."
Still, Heisbourg said that North Korea is "on their way" to acquiring that capability.
"It's a question of years it's not a question of decades," he said.
If authentic, Wednesday's test would mark the first North Korean nuclear test involving a hydrogen bomb. Hydrogen bombs have greater destructive capability than the atomic weapons dropped on Hiroshima and Nagasaki during World War II.
They're also much more difficult to make — which is why many analysts are viewing North Korea's announcement with a hefty dose of skepticism.
Why so skeptical?
A successful hydrogen-bomb test would undoubtedly be a massive coup in Pyongyang's quest to improve its still-limited nuclear arsenal.
However, Kim's claims to even have a hydrogen bomb have been quickly shot down in the past. Senior U.S. defense and intelligence officials poured cold water over his announcement in December that Pyongyang had developed a hydrogen bomb. Similar doubts were raised almost immediately after North Korea boasted that "heaven and earth" was shaking with its test on Wednesday.
For starters, experts say North Korea has a tendency to exaggerate its nuclear prowess and lacks the technological capability to produce a hydrogen bomb.
"I don't believe they detonated a hydrogen bomb," said Jin Canrong, an international relations expert based at Renmin University in Beijing.
He likened the seismic impact of the latest test to one in 2013 which involved an atomic weapon. "They might have detonated a miniature atomic bomb," Canrong added.
Heisbourg too said he'd be "very surprised" if this was a true hydrogen bomb. More likely, he said, was that North Korea had tested a "boosted device" on Wednesday — something "halfway between an ordinary Hiroshima or Nagasaki-type atomic weapon" and an H-bomb.
"North Korea is not as broadly developed as, let's say, India," Heisbourg added. "It does not appear that they have the ability to do a fully-fledged H-bomb because you need a much more broadly-based industrial capability and technical capability than the one North Korea currently has."
Even if it were a hydrogen bomb, North Korea would still have some ways to go before it was fully capable of using it in an attack. Hesibourg noted that the U.S. did "dozens" of tests before it gained the capability to put such weapons on rockets for operational delivery.
Should the U.S. be worried?
In short: Yes.
North Korea could acquire that capability within the next few years, according to Heisbourg.
"This is no longer something which is on a 10-year timescale," he said.
Given that North Korea has demonstrated a willingness not just to talk about but also to use force, analysts said there's reason for alarm. South Korea and Japan have immediate cause for concern — but the threat extends further.
"If you are China, if you are Japan, if you a country whose prosperity and security depends on your relationship with Asia-Pacific — which means most of the world — you are going to be very, very worried," Heisbourg said.
What happens now?
North Korea has remained technically at war with South Korea since a 1950-53 conflict ended in a truce. Pyongyang has repeatedly threatened to destroy the South — and Japan also is far from an ally.
Japan's Prime Minister Shinzo Abe called the test a "serious threat" to his nation's security which "cannot be tolerated," saying his country will take a "firm response."
Britain's Foreign Secretary Philip Hammond said a "robust international response" would be discussed by the United Nations Security Council members.
The body quickly called an emergency meeting over the nuclear claim. But while analysts expect a push for more — or better enforced — sanctions against North Korea, they say that ship may have sailed.
"The U.S. and the European countries essentially don't have any economic relations with North Korea so there are not sanctions which would have any sort of bite," Heisbourg said.
While some credit sanctions with helping bring Iran to the nuclear-weapons negotiating table, Iran had more to lose economically from its numerous partners. At this point, North Korea is mostly cut off.
"With Iran, we could develop a broad spectrum of sanctions which could be ratcheted up or down depending on the circumstances," Heisbourg said. "In the case of North Korea, we've pretty much used up everything in the locker — except for China."
He and other analysts called China the biggest player in the current game, but one in the precarious position of balancing concerns over North Korea's advancing nuclear program with worries about its state failure.
"The key actor here is China," said Timothy Stafford, research analyst on nuclear policy at the London-based Royal United Services Institute. "The last thing it wants is chaos on its border resulting in economic disruption or a migration crisis."
China has two moves: exert heavier economic pressure on North Korea as punishment or maintain the status quo for fear of provoking the nation's collapse, according to experts.
He said the question is how angry will China be at North Korea's decision to ignore warnings against a test.
While China has long been an ally of desperately poor and reclusive North Korea, experts noted that it too stands to lose from a nuclear escalation.
"This directly threatens China's national security, threatens the peace and stability of Northeast Asia and the region at large," said Professor Shi Yinghong, an expert in international affairs based at Beijing's Renmin University.
Analysts in China predicted Beijing would look outward in order to stave off a broader crisis, partially because it already has its hands full dealing with issues in the South China Sea and beyond.
"China will have to work with other partners on this issue," said Professor Zhu Feng, of Nanjing University.
In the meantime, Stafford suggested keeping an eye out for a possible shift in Washington's calculus.
While the U.S. might not currently face a direct threat, Wednesday's test adds weight to criticism that Washington's current North Korea policy is failing.
"North Korea shows no signs of wanting to return to the negotiating table, or to suspend its nuclear program, and is instead making tangible (if limited) advances," Stafford said in an email.
While that doesn't necessarily mean a near-term crisis, it does confirm North Korea is making progress towards a working H-bomb and eventually the ability to strike America.
"Preventing that eventuality is a priority for Washington, so look for the administration to start making further reassessments of North Korean policy to see how its efforts could be more effective," he said.
Still, analysts in China warned that North Korea could be looking to boost its leverage in negotiations with the U.S. — and be using the test as a bargaining chip.
"They hope to become a nuclear power to maintain their domestic dictatorship," Shi said. "They may also want to extract something, a nuclear blackmail."