An earthquake of magnitude 3.4 was detected in North Korea on Saturday, the Chinese earthquake administration said. This raised fears of another nuclear test from the isolated state, but South Korea and the Comprehensive Nuclear-Test Ban Treaty Organisation – a nuclear proliferation watchdog – said they believed it was a natural earthquake.

The quake occurred at 4.29 pm local time and was recorded at a depth of zero km, the Chinese agency said. The earthquake was centred 50 km away from North Korea’s Punggye-ri nuclear test site.

South Korea’s weather agency said it was analysing the nature of the earthquake. It initial opinion was that it was a natural earthquake because no soundwaves specific to a man-made earthquake were detected.

A South Korean official told Reuters: “A key method is to look at the seismic waves or seismic acoustic waves, and the latter can be detected in the case of a man-made earthquake. In this case, we saw none. So as of now, we are categorising this as a natural earthquake.”

Earlier this month, a 6.3 magnitude earthquake was reported after Pyongyang’s sixth underground hydrogen bomb test at the Punggye-ri site. The September 3 test caused an earthquake five to six times more powerful than the seismic activity recorded after the country’s previous nuclear test.

On Saturday, North Korean Minister of Foreign Affairs Ri Yong Ho had said Pyongyang could respond to Donald Trump’s threats of military action by testing a hydrogen bomb in the Pacific Ocean. “It could be the most powerful detonation of an H-bomb in the Pacific,” he told reporters in New York.