Experts and South Korean officials said North Korea’s nuclear test today was likely bigger than previous blasts in 2006 and 2009 and could be a six to seven kiloton explosion.

The rogue state is thought to have carried through on its threat to conduct an atomic test with seismic sensors detecting a magnitude 5 shudder in the vicinity of North Korea's testing range at midday local time.

Official confirmation that the tremor was due to a test had not been given, but the area of the shake is not prone to earthquakes and South Korea and Japan had convened emergency cabinet meetings and the UN Security Council was preparing to convene.

South Korea and the US placed their forces in South Korea on alert in the wake of the rumoured blast as reports emerged that North Korea may have yesterday given the US and China advance warning of the test.