North Korea conducts its most powerful nuclear test yet

North Korea conducted its fifth and potentially most powerful nuclear test, claiming to have successfully tested a nuclear warhead.

North Korea confirmed its latest nuclear test had confirmed that it could mount a nuclear warhead on a rocket, hours after the test was carried out.

"The nuclear test finally... confirmed the structure and specific features... of a nuclear warhead that has been standardised to be able to be mounted on strategic ballistic rockets," the state-run Korean Central News Agency said. 

A seismic tremor recorded in an area around North Korea’s known nuclear site on Friday, an activity that the South Korean government suspected to be a nuclear test.

The quake was detected near North Korea’s Punggye-ri nuclear test site as the country celebrates Foundation Day, which marks the anniversary of the founding of the nation in 1948.

“We believe that it was a nuclear test. We are trying to figure out whether it was successful. The blast measured about 10 kilotons,” a South Korean defence ministry spokesman was quoted as saying.

On Friday, the US Geological Survey picked up a tremor measuring 5.3, which South Korean officials said had the hallmarks of an earlier nuclear test that was carried out on January 6 at Punggye-ri.

Japan’s public broadcaster NHK reported the country’s defence ministry was preparing to dispatch aircraft to analyse air samples to see if any radiation could be detected.

“If North Korea conducted a nuclear test, that can never be tolerated. We must lodge a strong protest,” Japanese Prime Minister Shinzo Abe was quoted as saying.

North Korea has always insisted it will continue nuclear tests despite global condemnation and toughened sanctions.

North Korea has been under UN Security Council sanctions since it first tested an atomic device in 2006.