North Korea is thought to have produced enough plutonium for about six to eight weapons and has already produced one rudimentary nuclear device. It likely cannot miniaturize a nuclear weapon to mount on a missile and would need a significant amount of testing to master the technology, weapons experts say. And its Soviet-era bombers would not be able to evade the advanced air forces of the United States, Japan and South Korea to deliver a bomb, which means it may be many years before North Korea can actually threaten the world with a nuclear weapon.
North Korea's nuclear arms program is not a major security threat at present because it has not yet shown it can build an effective bomb, nor does it have an effective delivery system.
Results that show the explosive force of the current test should be known in the next few days, which will indicate if the country has improved its nuclear weapons technology.
The biggest security threats posed by the North come from its hundreds of mid-range missiles, which can hit all of South Korea and most of Japan, as well as its artillery batteries posted close to its border with the South. Jane's Defence estimated the North could rain 500,000 shells an hour into the Seoul area, which is home to about half of South Korea's 49 million people.
A North Korean first strike with artillery and rockets, which may also carry biological weapons or material to spread radiation poisoning, would cause major damage to economic powers South Korea and Japan, which in turn would deal a heavy blow to the global economy. But it would also be a suicidal move, because the U.S.-led counter-strike would quickly destroy North Korea.