Hong Kong called off two consecutive drone shows for safety reasons, a leading expert has said, after the cancellations sparked questions about how neighbouring Shenzhen went ahead with its performance.

As many as 330,000 people were left disappointed on National Day on Tuesday when a panda-themed drone performance set to precede a fireworks display was axed just a few minutes before its scheduled time.

Authorities announced the event was cancelled due to ionospheric scintillation, an astronomical phenomenon which is mainly caused by solar activities and leads to a poor GPS signal.

It was the second night in a row a drone show had been cancelled over the same factor.

Sky Yeung King-sheung, chairman of DNT FPV Drone Association, said on Wednesday that poor signal might cause drones to deviate from their designed locations and clash. The deviation would not be acceptable if it exceeded 10cm, he added.