Rainbow-coloured clouds in the shape of a stairway were seen in the skies above Hong Kong, wowing onlookers who spotted them hanging over Tsing Yi earlier this month.

Describing it as a “rainbow stairway to heaven”, the Observatory on Monday shared photos taken by a resident on its social media page and explained how the rare phenomenon was created.

“This is a result of the collaboration between distrails and iridescent clouds,” it said.

The photos were taken in Tsing Yi on October 4.

Distrails, otherwise called dissipation trails, refer to a gap between clouds after aircraft travel across shallow and broad clouds, according to the forecaster.

“The heat from the engine exhaust evaporates the water droplets within the cloud, creating a path just like the aircraft has essentially ‘carved out’ a line in the cloud,” the Observatory said.