PLYMOUTH, Maine — Firefighters battled a stubborn fire Thursday on Small Road.

Unlike the house fires they often are called upon to put out, this one involved farm machinery: a corn harvester.

“It was pretty well engulfed when we got there,” Plymouth Assistant Fire Chief Arrin Farrar said Thursday night.

According to Farrar, firefighters were called to a cornfield about 4:30 p.m.

“It was a pretty tough fire,” Farrar said. “We’re not sure how it started.”

At first, firefighters used water to try to extinguish the fire, then switched to foam, which did the trick, he said.

Diesel fuel ignited, causing what Farrar described as “liquid fire” to drip to the ground.

While the harvester was badly burned, crews managed to save its engine, Farrar said.

Neither the name of the harvester’s owner nor a damage estimate was available Thursday night.

A half-dozen firefighters and two firetrucks were involved in the 15-minute effort.