A US travel ban issued following the June death of US student Otto Warmbier, who was released in a coma after being held by Pyongyang for more than a year, will come into effect on Friday.

Britain updated its advice at the weekend to urge its citizens against "all but essential travel".

Japan's public broadcaster NHK cited diplomatic sources as saying the reason for the cancellation was unclear. It said there was speculation it could be part of the North's efforts to save fuel in the face of increasingly tough United Nations Security Council sanctions over its nuclear and ballistic missile programmes.

Last month Pyongyang tested two intercontinental ballistic missiles that appeared to bring much of the US mainland into range.

Oil is not currently subject to sanctions but fuel prices jumped in Pyongyang earlier this year, prompting suggestions that the rise was driven by a fear of restrictions being imposed.

Specialist tour agencies which had scheduled trips to the air show said they had cancelled them.

"We have indeed been informed that the Wonsan Air Festival has been cancelled," Stefan Goossens, a tour organiser at Netherland-based 4Aviation, told AFP.

Rayco Vega at China-based KTG DPRK Tours & Information, said that the agency has scrapped its plans. (AFP)