By Philippa Fogarty
North Korea's announcement that it has defied international warnings and carried out a nuclear test has drawn condemnation from around the world.
Pyongyang's move could potentially trigger a regional arms race
Japan has described the test as a "grave threat to our nation", while China expressed "resolute opposition" to the actions of its neighbour.
But with a nuclear North Korea apparently a new reality, attention is turning to what the long-term effect of the test might be in Asia.
Some analysts have warned that it could destabilise the East Asian region and trigger an arms race.
"I don't think we'll see an immediate domino effect with Japan and South Korea seeking to acquire nuclear weapons, but this certainly complicates the situation," says Dr Daniel Pinkston of the US-based Center for Non-proliferation Studies.
"The situation is very serious and it does have the potential. There would be a number of tit-for-tat steps. And each step of the way the choices that are made determine where we end up."
The first such step would lie with Japan, the nation conceivably most threatened by a nuclear North Korea, and where the test is likely to cause widespread shock and outrage.
Mr Abe has taken a tough stance towards Pyongyang
Tokyo has been steadily strengthening its strategic alliance with Washington, under whose protective military umbrella it shelters, since Pyongyang flew a missile over northern Japan in 1998.
It has signed up to the US missile defence system and upped its own defences against a North Korean missile threat, while relying on US-led diplomacy to contain North Korea.
But with the US occupied in the Middle East, and with no sign of concessions from Pyongyang, Japanese concern could grow.
"If we see North Korea with demonstrable nuclear weapon capability and [they] turn it into something that could go on a missile, and if the US stance towards the North is perceived as weak, then the Japanese would get very nervous," says Dr Chris Hughes of the University of Warwick in Britain.
Nonetheless, says Dr Hughes, Japan's most likely move would be further sanctions, both via the UN and its own unilateral measures, aimed at forcing North Korea to return to dialogue.
In parallel, Japan could also look at acquiring its own defence capability - such as Tomahawk missiles - that could target North Korea's missile bases.
But even then, a move to nuclear weapons would be something else entirely.
The nuclear topic has been sacrosanct in Japan for decades and the Japanese public remains vehemently opposed to becoming a nuclear power.
Seoul has cautioned against pushing Pyongyang into a corner
While Japan's hawkish new Prime Minister Shinzo Abe has won popularity with his tough stance towards Pyongyang and calls for a more assertive foreign policy, persuading Japanese people that they need nuclear weapons would be a tough task.
Equally, Mr Abe will be aware of legal constraints - such as the NPT - that prevent Japan having nuclear weapons, and also of the considerable international opposition, not least from main ally the US, to such a move.
"Abe will be tempted for domestic reasons and national security reasons to jump up and down," says Dr Hughes. "But he knows he has to tread a fine line."
Any move by Japan would have a knock-on effect on the region.
"There is no way that a South Korean leader could sit by idly while Japan [is being] nuclearised," says Dr Pinkston.
There would be popular support for this - a poll in 2005 by South Korean daily Joongang Ilbo showed that two-thirds of respondents believed South Korea should possess nuclear weapons.
And with Japan and South Korea set on such a path, China, until now the region's only nuclear power, could then move towards modernising and upgrading its own arsenal, potentially triggering a similar response from Taiwan.
This is the scenario that concerns diplomats - a nuclear north-east Asia still struggling with long-standing historical grievances, territorial disputes and rows over oil and gas.
But an arms race - and its political and economic consequences - is not something that countries are seeking.
"Anything that causes regional instability is not in China's interests," says Dr Pinkston.
Beijing needs stability so that it can focus on its economic development, he says.
Any economic dip could impact badly on a society already coping with rapid change and severe income disparities.
Popular unrest is one of the Chinese political elite's greatest concerns and so maintaining a stable society is the priority, he says.
Countries around the region will more likely put considerable effort into pursing a diplomatic course rather than moving rapidly to arm themselves further.
A North Korean nuclear test could, in fact, be the foundation for better regional dialogue and a more unified effort to put pressure on Pyongyang, says Nicholas Szechenyi of the Washington-based Center for Strategic and International Studies.
Mr Abe has already held a top-level summit with Chinese President Hu Jintao after a five-year suspension under his predecessor, Junichiro Koizumi, and he is now in Seoul for talks aimed at improving ties.
"It is very easy to leap to the notion of an arms race in the region, but from Japan's perspective, preventing the spread of weapons is the main objective," Mr Szechenyi says.
He cites the effort at the UN to create a multilateral response to North Korea's announcement that a test was planned as an example of tighter regional co-operation.
The concern of all parties is to prevent proliferation," he says. "An arms race is in nobody's interests."