The huge white mass is seen rolling across the sands of Albufereta beach, obscuring everything in its path – despite an otherwise cloudless sky.
Some speculated that the cloud was smoke from a fire, while others compared the apocalyptic scenes to the smoke cloud left behind when thousands of firecrackers are set off for the Las Fallas festival in neighboring Valencia.
Spanish local Antonio Carlos Soria Hernandez posted the film showing the unusual phenomenon on his Facebook page and it soon went viral, with thousands of people sharing the short video.
Tourists and locals from other coastal towns in eastern Spain also reported similar cloud masses in Calpe, on the Costa Blanca, and the popular resort of Benidorm.
WATCH: YouTuber captures huge cloud engulfing Alicante.
It was explained as a phenomenon that occurs when the cold sea meets the warmer air from inland, causing a huge cloud to form.
When the video was posted on Facebook, one user commented: ‘I thought it was a fire’.
Mr Hernandez, who filmed the scenes, agreed, explaining: ‘I saw it and ran down thinking it was exactly that… a fire and caught it on camera, the effect of the cloud is really beautiful.’ – Daily Mail.