The roll cloud, also known as an arcus cloud, moved over the city between 8am and 8.30am.

Lyndoch resident Leigh Fawcett managed to grab his camera and shoot some photos of the cloud but was disappointed it moved through the city so quickly.

East Warrnambool mother Kelly Lynch also captured the spectacle from her backyard with some amazing photographs.

"Our seven-year-old daughter Georgia thought it was very scarey and ran inside," Mrs Lynch said.

"She's seen shows about tornados on the television."

However, her two young sons, Charlie, 5, and Cooper, 2, were awe-struck. "They thought it was cool."

South Warrnambool resident Bill Fish noticed the cloud starting to form as he was out on his morning walk.

He raced home and took a photo from his front veranda looking west towards the Merri River flats.

"It was just so unique. I've never seen anything like it in my life," Mr Fish said.

"I printed the photo out and my wife saw it and thought it looked like a tornado."

Marcus Green was driving to work along Stanley Street and came to stop in the middle of the road when he saw the sky.

"It was spinning like a horizontal tornado," Mr Green said.

According to the Bureau of Meteorology, long cloud formations like roll clouds are rare as they require uniform cloud formation along an extended front.

"Roll clouds usually form near advancing cold fronts, whose down-draft causes moist warm air to rise, then cool below its dew point and thus form a cloud," the bureau's technical officer John Cornall-Reilly explained.