Update | China summons North Korean ambassador after claims of successful H-bomb blast

North Korea announced today it had successfully tested a hydrogen bomb – generally much more powerful than an atomic bomb – which, if confirmed, would mark a stunning step forward in its nuclear development.

READ MORE: Don’t believe the hype: Nuclear experts remain sceptical about North Korea’s hydrogen bomb claims

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

“With the perfect success of our historic H-bomb, we have joined the ranks of advanced nuclear states,” the announcer said, adding that the test was of a “miniaturised” device.

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 so that it could fit on a ballistic missile.

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

But North Korea’s close ally China has not delivered an early birthday present to the Hermit Kingdom leader.

China, North Korea’s key diplomatic protector, said Wednesday it “firmly opposes” Pyongyang’s nuclear test, adding it was carried out “irrespective of the international community’s opposition”.