SEOUL- Japan has concluded that tremors detected in North Korea were a nuclear explosion, marking the sixth atomic test by Pyongyang since 2006.

A shallow, magnitude-6.3 quake shook North Korea, hours after the reclusive state said it had developed an advanced hydrogen bomb that possesses “great destructive power”.

The tremor struck within a kilometre of the site of a magnitude-5.3 “nuclear explosion” from September last year, according to the United States Geological Survey (USGS).

The quake was only 10km deep, the US Geological Survey said, again suggesting a nuclear device.

It is bound to increase the tension hours after United States President Donald Trump and Japanese Prime Minister Shinzo Abe talked by phone about the “escalating” nuclear crisis, reports ABC news.

Japanese Foreign Minister Taro Kono said they had examined the data from the tremors and “concluded that it was a nuclear test”, while Mr Abe said Japan was speaking to other nations.

“I have already instructed the related ministries to collect and analyse intelligence, to give people of Japan informed appropriately, as well as to liaise with the related nations such as the US, South Korea, China and Russia,” he said.

Witnesses in the Chinese city of Yanji, on the border with North Korea, said they felt a tremor that lasted roughly 10 seconds, followed by an aftershock.- Agencies