The Westport Fire Department responded to the fire at 265 Main St. at 2:50 a.m., said a fire department statement.
A "heavy fire" had engulfed the barn when firefighters arrived, the statement said.
Upon arrival, fire companies laid a supply line to a nearby hydrant and quickly knocked down the blaze, the statement said.
Crews then conducted search-and-salvage operations of the building. No injuries were reported.
Fire departments from area towns were also called to the scene and to cover Westport Fire Headquarters.
Units remained on scene until the early morning hours extinguishing hidden fires, conducting salvage operations and securing the structure.
Westport Fire officials are investigating the cause of the blaze and will be remaining on the scene until the investigation is complete.
The reason for the fire was undetermined as of Thursday morning.
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