The blaze broke out on disused land near Gort na Greine.
The fire was quickly brought under control as Gardai sealed off the area.
One eye-wtiness told donegaldaily.com: “It’s hard to know if it was started deliberately or not but the fire was brought under control very quickly.
“Local people called the fire brigade out as the fire was getting close to a trailer parked there.”
Garda sources say they are investigating how the fire started, with fire officers assisting.
“It was very close to a container and was spreading to another,” said one source.
“We are suspicious about its cause at this stage.”