No confirmation yet from any intelligence agency or watchdog group. Even the seismic scientists haven't said anything registered. All this might simply be a propaganda ploy by NK. Relax. No time to panic.
Indeed it is not good news. If this could have been forstalled by the US conducting bi-lateral talks with Nth Korea as they have been demanding, why the bloody hell not do so. Talking costs nothing.
The danger is not just Nth Korea. There will be elements in Japan advocating acquisition of a nuclear deterrent. Probably won't happen, but I very much doubt that any country in east or south east asia would be comfortable with a nuclear armed Japan. Memories are not that short.
The worst case scenario is a nuclear arms race in the region.