Dion Costigan was watching his boys skate in Eaglehawk, in central Victoria, when he turned and saw something in the sky like nothing he had ever seen before.

"I just thought, wow!" he said on Saturday morning.

"The line, the formation of clouds just had amazing colours in it, these light greys all the way down to black."

Bureau of Meteorology senior forecaster Tom Delamotte said the cloud mass Mr Costigan and many other social media users captured was a shelf cloud formation.