BENTON — State fire investigators were called late Thursday afternoon to help determine the cause of a fire that heavily damaged a vacant house on Unity Road in Benton.

The house at 864 Unity Road was ablaze when firefighters arrived at the scene, according to Travis Leary, chief of the Fairfield and Benton Fire-Rescue Department, who was at the scene.

“At 3:50 p.m., we got called and there was heavy fire stirring on four sides of the building on the first floor, and in and out of the roof as well,” Leary said. “We did an exterior attack only.”

About 20 firefighters from Fairfield-Benton, Albion, Fairfield, Unity and Winslow worked at the scene, and Waterville firefighters covered the fire station in Fairfield, according to Leary. The Kennebec County Sheriff’s Office, Clinton Police Department and Delta Ambulance were also at the scene.

“One firefighter was treated for heat exhaustion, but he’s OK and was not transported,” Leary said, adding that the firefighter who was treated was from his department.

Leary said he spoke to the son of the former owner of the property and was told the house had been vacant for at least six years. The wooden house, which appeared to have two floors and a basement, had additions built onto it.

The house is located down a steep embankment off the road and surrounded by another building, an old camper, truck and other equipment. The property is thick with oak and pine trees, bushes and tall grass.

Two investigators from the Office of State Fire Marshal arrived at the scene, as did the state’s new fire marshal, Shawn Esler, the former Waterville fire chief who lives in nearby Albion, about 15 minutes away.

Esler, who began his new position Sept. 23, said fire investigators responded to the scene at the behest of Leary.

“We’re fortunate to be able to see it at the latter stage of suppression efforts,” Esler said. “We’ll go to work once the fire is extinguished and determine a cause.”

Traffic heading from Benton to Unity was at a standstill for at least an hour because the road had been blocked at the fire scene, though vehicles traveling from Unity toward Benton was able to get through.

Many motorists said they were anxious to get through.

One woman said she is a health care workers and was trying to get to Belfast to care for an elderly patient. Another woman said she was trying to get home.

One man was playing a guitar to pass the time while sitting in the driver’s seat of his car.