"The republic's first hydrogen bomb test has been successfully performed at 10:00am on January 6, 2016, based on the strategic determination of the Workers' Party," a state television news reader announced.

The surprise test was personally ordered by North Korean leader Kim Jong-Un and came just two days before his birthday.

Only last month, during remarks made during an inspection tour, Kim had suggested Pyongyang had already developed a hydrogen bomb - although the claim was greeted with scepticism by international experts.

A hydrogen, or thermonuclear device, uses fusion in a chain reaction that results in a far more powerful explosion. The announcement will leave the international community scrambling to verify the accuracy of the North's claims.

Most experts had assumed Pyongyang was years from developing a thermonuclear bomb, while assessments were divided on how far it had gone in mastering the technology to miniaturise a device that could fit on a ballistic missile.

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