Dozens of reporters from China, the United States and Russia departed on a charter flight from Beijing, according to Chinese state broadcaster CGTN which is part of the contingent. It showed the journalists board a small plane emblazoned with the North's flag.

The journalists will cover the demolition of the Punggye-ri nuclear testing site inside a mountain in the northeast of the country, which is scheduled to take place between Wednesday to Friday.

Agence France-Presse and some other major media organisations were not invited to cover the event.

The North has staged all six of its nuclear tests there beginning in 2006. The latest and by far the most powerful in September last year was said by Pyongyang to have been a hydrogen bomb.

The North previously said South Korean journalists would be allowed to attend this week's ceremony, as part of a series of ice-breaking diplomatic moves following a summit between the two country's leaders last month.

But Pyongyang refused at the last minute to accept a list of South Korean journalists. It has railed against the ongoing "Max Thunder" military aviation exercise involving the United States and South Korea, calling it "an act of provocation."

Pyongyang has also threatened to cancel a summit between US President Donald Trump and its own leader Kim Jong Un in Singapore on June 12, despite weeks of tentative rapprochement.

The North has accused the US of cornering it with a unilateral demand for denuclearisation.