North Korea is suspected of conducting their biggest nuclear weapon test yet, after a 4.9 magnitude seismic reading was recorded in an area that is not prone to earthquakes.

The North Korean regime is yet to confirm reports by South Korean media that the blast was caused by nuclear weapons testing.

The latest suspected blast follows previous tests in 2006 and 2009.

Here are some expert reactions to the news:

Associate Professor Tilman Ruff, Nossal Institute for Global Health, University of Melbourne

This is extremely unwelcome news. It’s not surprising, given the build-up of anti-US rhetoric from North Korea in recent weeks and talk about potential missile launches and a possible nuclear test. The timing, just before President Obama’s State of the Union address, was also widely predicted. All of the information available suggests it was a nuclear test. North Korea has for some time now been the only nation conducting explosive nuclear testing for the purpose of trialling and developing nuclear weapons.

It’s been known for quite some years that North Korea has a reprocessing program to separate plutonium from spent reactor fuel (that’s one of the two materials that can be used to build nuclear weapons) and that’s believed to have been used in the first two nuclear explosions in 2006 and 2009.

Both materials, particularly plutonium, were thought to be technically unsuccessful, and quite likely didn’t perform as planned.

It has since come to light that North Korea has a uranium-enrichment program, which is likely to produce highly enriched uranium, which is the other material that nuclear weapons can be built from. Most modern nuclear weapons combine plutonium and highly enriched uranium.

If North Korea were able to produce enough highly enriched uranium and turn it into a weapon, it would signify a significant step in their technical capacity to build nuclear weapons.

The very clear message this sends is that the issue of nuclear weapons has not gone away and that nuclear proliferation is not under control. There is a very urgent need to deal with nuclear weapons and outlaw and eliminate them as rapidly as possible.

In the short term, from a political point of view, North Korea is clearly doing this to increase its political bargaining position, presumably for some domestic political purposes as well, to assert the authority of a new leader and to assert their technical capacity.

It will be very important for China and the United States have a consistent position that really does put significant pressure on North Korea. Getting really serious about disarmament will undermine the rationale and drivers for proliferation by North Korea and others.

Underground testing shouldn’t involve the release of radioactivity. But there have been underground nuclear tests that have vented nuclear material (where the exposition hasn’t been contained and radioactive materials have been spewed into the atmosphere). Hopefully, that hasn’t occurred here but I’ve heard no such reports one way or the other yet.

Of course, a nuclear explosion generates radioactive waste and in a geological environment that has been fractured by the explosion itself, those radioactive materials could leak into the ground water and potentially eventually contaminate water supplies and soils. That really depends on the geology – on how deep the explosion was and how effectively it has been contained.

It’s certainly not a good thing from a health and environmental point of view but it’s significantly less of an issue than the immediate atmospheric testing of the 50s, 60s and 70s.

Dr. Benjamin Habib, Lecturer in Politics and International Relations at La Trobe University.

I am assuming this is a test. You don’t get magnitude 4.9 readings in that area from earthquakes. I have been there, it’s not a seismically active region.

The technical reasons for the test could be that this is the first time they have tested a uranium-based nuclear weapon. Their previous tests have been with plutonium-based devices, which are technically more rudimentary.

The advantage with uranium is you don’t have to go through as many industrial processes. A uranium-based weapon is technically more sophisticated.

Overall, I don’t think it really changes anything. We know they are a nuclear weapons power.

The nuclear program is so deeply embedded in the politics and the economy of the regime, it would be immensely difficult for a leader to give it up, even if they wanted to.

This is the highest reading so far. The previous one in 2009 was around 4.52. The 2006 explosion was a dud.

As far as Australia is concerned, there’s no threat to us. I don’t think North Korea is going to fire off nuclear weapons at anyone. The whole point of having them is to deter other people from attacking them.

This is a state and nation that has felt under siege since the Korean war and they see the US threat as an imminent one. Their nuclear proliferation makes sense to them.

It’s not even clear if they can deploy these bombs on missiles yet. Even if they could, how many would they have compared to what the US has got? A first strike by the North Koreans would make no sense at all.

But it does fuel an arms race in the region.

Dr Bruce Jacobs, Professor of Asian Languages and Studies, Monash University

I think the world has gotten pretty good figuring out what are earthquakes and what are nuclear explosions, so yes, I think we should be taking this seriously.

The North Koreans have certainly threatened to conduct such a test and this is consistent with past behaviour.

We should be concerned on a number of levels.

Nuclear weapons are horrendously destructive and in a place like East Asia with very densely concentrated populations, they pose a considerable danger.

The other thing is that the North Koreans are spending all their money, huge funds, on nuclear weapons and long range missiles which would be better spent feeding their people. They have tremendous levels of starvation, tremendous costs and it is very sad.

It’s disheartening news on many levels.

It’s difficult to predict what will happen next. The North Koreans have been part of the Six Party Talks but haven’t paid much attention to that.

They see this as in their interests. They are saying, ‘We are big boys, don’t muck with us.’

It’s sending a message to the US, to Japan, the South Koreans, the Chinese too and the Russians.