Experts differ about the scale and immediacy of the military threat posed by North Korea's latest nuclear test, but there is little disagreement about the alarming proliferation risks it presents.

The most pressing concern is that cash-strapped North Korea will become a one-stop shop, selling nuclear material, technology and even weapons to other countries, terror groups, or states seen as sponsoring terror.

And there is also a fear that the North's nuclear weapons and ballistic missile programmes will prompt others in the region to reconsider their non-nuclear status, causing the entire non-proliferation regime to unravel.

North Korea has clear form as a proliferator, notably in the sharing of missile technology with Iran, but also in helping Syria build the nuclear reactor that was destroyed by Israeli warplanes in 2007.

"Nuclear terrorism is the thing we worry most about in the United States," said Robert Gallucci president of the MacArthur Foundation and a former US assistant secretary of state.

"The prospect that the North will sell highly-enriched uranium, nuclear weapons designs or even nuclear weapons to all comers, is not a happy thought if you live in one of America's cities," Gallucci told a nuclear security forum in Seoul on Tuesday.

A key unanswered question arising from the North's test on February 12 concerns the type of fissile material that was used.

South Korean, Japanese and UN monitoring efforts have so far failed to detect any tell-tale radioactive fallout, but many experts believe the North detonated a uranium device for the first time.

Its two previous tests in 2006 and 2009 had both been of plutonium bombs, and a confirmed switch to uranium would fuel proliferation concerns.

Highly-enriched uranium is seen as the "preferred currency" of rogue states and terror groups. It is the easiest fissile material from which to make a crude bomb and uranium enrichment technology can be readily transferred and sold.

"If the test turns out to have been uranium based then I think we are entering a whole new game in terms of proliferation risk," said Choi Kang, a security expert at the Korea National Diplomatic Academy.

"And it's a risk that extends the North Korea threat beyond the Korean Peninsula and beyond the Northeast Asian region," Kang said.

Iran features prominently among the list of North Korea's potential clients put forward by analysts, and there were numerous reports -- denied by Tehran -- that Iranian experts were on hand to observe last week's test.

Graham Allison, director of the Belfer Center for Science and International Affairs at the Harvard Kennedy School, also notes that Al-Qaeda leader Ayman al-Zawahiri has been seeking nuclear weapons for more than a decade.

"In intelligence circles, North Korea is known as "Missiles 'R' Us," Allison wrote in a New York Times editorial.

With last week's test, North Korea was announcing it has "a new cash crop", Allison said, calling for an unequivocal US proliferation warning -- backed by the threat of force -- to North Korean leader Kim Jung-Un.

"The urgent challenge is to convince him and his regime's lifeline, China, that North Korea will be held accountable for every nuclear weapon of North Korean origin," he said.

The scenario that ends with the detonation of a "dirty bomb" in a city like New York invokes the conventional proliferation plot of selling and smuggling nuclear material.

But analysts also stress the threat that North Korea poses to the global non-proliferation regime simply by its existence as a de facto nuclear weapons state.

The North's latest test was its largest yet in terms of explosive yield and, according to Pyongyang, marked a breakthrough in its efforts to develop a "miniaturised" warhead that could fit on a ballistic missile.

The further the North progresses towards a genuine nuclear weapons capability, the louder the questions coming from its neighbours about the need for their own genuine deterrent.

In South Korea, a number of ruling conservative party lawmakers have already called for a debate on withdrawing from the nuclear non-proliferation treaty (NPT) and embarking on a weaponisation programme.

"There a real danger of a domino effect here," said Lee Jong-Hoon, an international studies professor at Seoul's Yonsei University and a former National Security Council adviser.

"I think the message we should send to China is that it has to do more right now to prevent North Korea going any further," Lee told AFP.

"Otherwise the consequences might be a nuclear South Korea, a nuclear Japan and even a nuclear Taiwan. Is that what Beijing wants?"