The fire broke out at a large barn and workshop near Hatt late last night, said crew from Saltash.
Six fire engines and crew together with two water carriers and the Devon aerial ladder platform were scrambled to the fire.
The incident has now been scaled back, said Cornwall Fire and Rescue Service, with two fire engines and crew remaining on scene.
During the night, Saltash Community Fire Station posted this message:
"We are currently on scene at a large barn and workshop fire near Hatt. Six Pumps from Saltash, Callington, Camels Head, Crown Hill and Greenbank along with the Devon ALP and two water carriers (Liskeard & Plympton) are in attendance.
"Great progress is being made and the fire has been restricted from spreading further.
"Going to be a long night!"