A Sydney photographer has captured a rarely-observed rainbow cloud phenomenon called “iridescent clouds”.

Maria Milford was driving to the Gold Coast when she spotted the iridescent clouds over the sky in Woolgoolga, NSW.

She quickly whipped out her camera to capture the phenomenon, which she said lasted a couple of hours. 

How rare are iridescent clouds?

The Bureau of Meteorology said while the phenomenon isn’t a rare occurrence, it is rare to observe it.

The phenomenon happens randomly and there’s no “best” time of day to spot it – it can even occur at night.

It can be seen when the sun or moon is at a specific relative position to the observing person and the cloud coverage.

“The effect is not uncommon, although the brightness of the sun itself can make it difficult to observe at times,” a BoM spokesperson said.

“Iridescence can also be observed in clouds around the moon, but the effect is typically more muted.”

The Bureau warned people should not look directly at the sun, as it can cause eye damage. 

“Individuals should exercise caution when witnessing such events, as you are staring directly at the sun, even though it may be temporarily obscured by the cloud.”