North Korea claims nuclear test

"The field of scientific research in the DPRK (North Korea's official name) successfully conducted an underground nuclear test under secure conditions on October 9 ... at a stirring time when all the people of the country are making a great leap forward in the building of a great prosperous powerful socialist nation," KCNA reported."

"It said the underground test, carried out in defiance of international warnings, was a success and had not resulted in any leak of radiation.

The apparent nuclear test was conducted at 10:36 a.m. (1:36 a.m. GMT) in Hwaderi near Kilju city, South Korea's Yonhap news agency reported, citing defense officials.

Japan's Prime Minister Shinzo Abe said the test was "unpardonable", while China denounced the action as "brazen".

 The White House said the test, if confirmed, would constitute "a provocative act".

Sources: BBC NEWS - CNN - Herald Tribune - IAEA about DPRK - North Korea's nuclear program on Bulletin of the Atomic Scientists 

Lots of background and history: Think Progress: North Korea’s Atomic March

Experts warn of an accidental atomic war

"Pentagon project to modify its deadliest nuclear missile for use as a conventional weapon against targets such as North Korea and Iran could unwittingly spark an atomic war, two weapons experts warned Thursday.

Russian military officers might misconstrue a submarine-launched conventional D5 intercontinental ballistic missile and conclude that Russia is under nuclear attack, said Ted Postol, a physicist and professor of science, technology and national security policy at the Massachusetts Institute of Technology, and Pavel Podvig, a physicist and weapons specialist at Stanford." More via Infowars.com

And now we impose some more sanctions so even more Koreans can starve to death, Kim doesn't care, and a lot of other Asian countries will make there own nuclear bombs... But who cares.