North Korea's nuclear test is unlikely to spark a nuclear arms race in Asia, but analysts say Japan and South Korea may seek to beef up their missile defences and pre-emptive capabilities against the secretive state.
Pyongyang's second nuclear test came weeks after it fired a long-range rocket that flew over northern Japan, a clear message that North Korea is developing a nuclear weapon and the means to deliver it.
But analysts say North Korea's actions are defensive, while its neighbours are already under a US deterrent.
"The barriers to developing nuclear weapons are extremely high and both countries come under the US nuclear umbrella, so the chances of them actually developing nuclear weapons are slim," said Shi Yinhong, an international security expert at Renmin University in Beijing.
President Barack Obama was quick to reaffirm the US commitment to the defence of both South Korea and Japan yesterday, perhaps in a sign of Washington's concern that both countries stay out of the nuclear club.
"At the end of the day, what do nuclear weapons buy North Korea?" asked Brad Glosserman of Hawaii-based think tank Pacific Forum CSIS. "It buys them a deterrent. It allows them to say 'you can't come after us'. But I don't see how North Korea can use it to extort anything. It has a limited number of weapons and it has to know that if it uses them, it's 'game over'."
Few in neighbouring Japan are calling openly for the development of nuclear bombs, though some security hawks say the idea should at least be debated.
South Korea's biggest daily Chosun Ilbo yesterday urged the government to go nuclear, but analysts say it, too, is unlikely to risk alienating the US by doing so.
Instead, Seoul may seek to extend the range of its arsenal of missiles, currently limited to 300 kilometres, in an effort to counter the North's mid-range missiles.
"The much more real proliferation risk is that the North Korea test will encourage Japan and South Korea to accelerate developing missiles and missile technology," Renimin University's Mr Shi added.
"In a Northeast Asia arms race, missiles would be a much bigger risk than nuclear weapons," he said.
The test has already prompted a policy change in Seoul.
South Korea announced yesterday it was joining a US-led initiative aimed at intercepting shipments suspected of carrying equipment for weapons of mass destruction.
It marked the end of a drawn-out debate in Seoul whether to join a naval exercise that brings together 100 countries worldwide and risks angering North Korea.