A large earth tremor has been detected in North Korea, raising speculation that the country has carried out its sixth nuclear test.

U.S. Seismologists said the 6.3 magnitude quake was recorded at a depth of 10 km.

South Korea immediately convened a National Security Council meeting.

The tremor comes hours after North Korean Leader Kim Jong-UN was pictured with what state media said was a new type of hydrogen bomb.

State media said the device could be loaded on to a ballistic missile. Neither claim could be independently verified.

International experts say the north has made advances in its nuclear weapons capabilities but it is unclear if it has successfully Miniaturised a nuclear weapon it can load on to a missile.

South Korea officials said the quake took place in Kilju county, where the north’s Punggye-Ri nuclear test site is situated.

China’s earthquake administration described the tremor as a “Suspected Explosion”.

North Korea carried out its last nuclear test in September last year.

It has defied U.N. Sanctions and international pressure to develop nuclear weapons and to test missiles which could potentially reach the mainland US.

North Korean state news agency KCNA said Kim Jong-Un had visited scientists at the nuclear weapons institute and “Guided the work for nuclear Weaponisation”.

A series of recent missile tests has caused growing international unease.

North Korea has carried out a series of missile tests in recent months, including weapons that put the mainland us in range.

Last week it fired a missile over Japan in a move Prime Minister Shinzo Abe called an “Unprecedented” threat to his country.

North Korea has also threatened to fire missiles towards the US pacific territory of Guam.