GORHAM, N.H. — A wildfire burning southeast of Gorham, New Hampshire, has become the largest in the history of the White Mountain National Forest, covering an estimated 856 acres near the Maine line, NHPR reported Thursday, citing fresh mapping by the forest.

Crews had the Wild River Fire about 11% contained as of Nov. 5, NHPR reported. Forest Service spokesperson Jessie Dubuque told the station that no fire this big has burned there since the forest was created. Federal officials believe people started it, though they have not determined a cause, and they say no prescribed burns have been set in the forest recently, according to NHPR.

The fire was spotted Nov. 1 on the Androscoggin Ranger District in Coos County, about a mile west of the state border, and it moved fast across steep, rough ground in dry weather, Connecticut Public reported. Drought has left the woods full of dry leaves, dead wood and spruce and fir that burn easily.

About 90 federal firefighters, including at least 89 from the Forest Service, are fighting the blaze with three helicopters and a drone, NHPR reported. To reach it, they must wade across the Wild River, and a Forest Service road badly damaged three years earlier has made access harder. A spokesperson told NHPR on Thursday morning that crews were gaining ground steadily.

A closure order keeps the public out of the fire area so firefighters and emergency crews have safe access. It shuts all of Wild River Road and the Shelburne Trail, along with parts of High Water Trail and other trails.

No homes are close by, NHPR reported, and the Forest Service says the fire poses no significant threat to private property or public safety. Gorham Fire Chief Philip Cloutier told NHPR that a fire this size is unusual locally; the largest one residents can recall burned just under 100 acres, more than 20 years ago.

The Forest Service asks drivers who run into smoke to slow down and turn on their headlights, and asks people to keep personal drones away from the fire.