Firefighters were caleld out to a barn at Tretharrup near St Martin after a report of 40 tonnes of hay on fire.
Crews from Mullion, St Keverne and Helston attended just before 8.30pm after a report of the hay smoulding in a barn measuring five metres by 20 metres.
A fire service spokesman said: "The barn was full of large bales and firefighters wearing two breathing apparatus used two jets and two hose reels to extinguish the fire. The cause is believed to be accidental and confined to the barn."
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