SKOWHEGAN — Firefighters from several towns worked for hours Thursday to extinguish a fire in a conveyor belt gearbox at the Sappi Somerset Mill wood yard that was difficult to access because it was surrounded by piles of wood chips, a fire official said.

“There was a fire in a mechanical portion of a conveyor system that moves chips for the Sappi processes,” Skowhegan fire Chief Ronnie Rodriguez said Thursday.

Sappi officials called the fire department around 4:15 a.m. to request help with the fire, to which Madison, Canaan, Norridgewock, Fairfield and Waterville firefighters also responded, Rodriguez said. The last crews left the scene around 3 p.m., 11 hours later.

“We think something happened in the gearbox but I can’t say that was the determining factor,” he said. “Some of the mechanics of the conveyor belt’s gearbox started the fire.”

He said wood chips are piled about three stories high in the wood yard before they are placed on the covered conveyor belt system, which extends from 10 feet in the ground to about five stories in the air. More than 300 trucks a day deliver wood to the yard, he said.

Rodriguez said heavy equipment was used to move the piles of wood chips around the conveyor system so firefighters could access the fire. The conveyor belt itself was not on fire, he said.

“The entire encapsulation is about 6 feet wide and the conveyor belt takes up maybe 3 feet of that,” he said.

In describing the scene, he said to “picture Hannaford’s checkout belt going four or five stories in the air and you have a 2-foot catwalk right beside it and you’re trying to fight fire in there.”

The belt itself is covered by metal shaped like a semicircle; the belt was about 150 feet long but firefighters were dealing with only about the last 75 feet, he said.

About 20 firefighters joined several members of Sappi’s safety and fire brigade to fight the fire, Rodriguez said.

“Tip of my hat to Sappi for the help, and other mutual aid companies for their help, and it’s all about teamwork,” he said.

A sprinkler system activated, causing one of the firefighters’ access points to fill with water, he said.

Firefighters worked in temperatures that were in the lower single digits. No one was hurt, he said.

A spokesman at Sappi North America’s Boston headquarters did not respond to emailed questions Friday.