The waterspout tornado was seen over the sea at Polruan this afternoon.
A video posted by @KWTWeather on Twitter caught the incredible sight.
It comes as roads in Cornwall and Devon flooded in the early hours of this morning.
Heavy rain and thunderstorms are set to hit parts of the UK for the second day running.
The Met Office has issued several thunderstorm warnings for across the UK until the end of Wednesday.
Meanwhile, the Environment Agency has put out 19 flood alerts in areas of the Midlands and south-east England.
This follows a heatwave last week which left land parched and sparked fears of a drought in parts of the country.