Canberra, January 7, AZERTAC
Several governments promised a firm response as tensions soared, with many calling for further action by the United Nations against North Korea, which is already subject to an array of international sanctions.
The UN Security Council was to hold an emergency session later.
Australian Foreign Minister Julie Bishop has also made a statement related to the N Korea H-bomb test and called on for serious steps against the Democratic People's Republic of Korea (DPRK).
She said her country "condemns in the strongest possible terms" the test, which "confirms North Korea's status as a rogue state and continuing threat to international peace and security", adding that Canberra would express its concerns to Pyongyang directly and call for stronger UN sanctions.
The test, which came just two days before leader Kim's birthday, was initially detected by international seismology monitors as a 5.1-magnitude tremor next to the North's main Punggye-ri nuclear test site in the northeast.
Last month Kim suggested Pyongyang had already developed a hydrogen bomb.
The claim was questioned by international experts and there was continued skepticism over Wednesday's test announcement.
Whether an H-bomb or not, it was North Korea's fourth nuclear test and marked a striking act of defiance in the face of warnings that Pyongyang would pay a steep price if it continued pursuing its atomic weapons program.