HARDWICK — Firefighters from New Jersey and from the National Park Service were atop Mount Tammany, on the New Jersey side of the Delaware Water Gap, on Sunday night battling a forest fire of unknown origin.

The blaze broke out in mid-afternoon on a sunny mid-50s day that likely saw hundreds of people hiking to the top of the New Jersey side of the Delaware Water Gap National Recreation Area.

Just before sunset, a helicopter from the New Jersey State Forest Fire Service dropped some loads of water on the blaze, but by sundown, the fire had yet to be brought under control.

Kathleen Sandt, a spokesperson for the Delaware Water Gap National Recreation Area, said the helicopter had to cease operations after sundown as it was too dangerous to fly in the dark.

Fighting the fire on the ground were members of the state Forest Fire Service as well as specially trained personnel from the park. Sandt said volunteer firefighters were at the base of the mountain filling up backpack tanks of water and ferrying them to the top of the 1,526-foot peak.

The area of the fire is split between Worthington State Forest and the Delaware Water Gap National Recreation Area. Sandt did not know where the majority of the fire was in relation to the boundary.

The top of Mount Tammany is part of the Appalachian Trail. Over the years, a limited number of access paths have been cleared in the area. However, Sandt did not know if any mobile equipment could reach the fire scene along those paths.

Sandt said the red-dot and the blue-blaze trails on the mountain will be closed until the fire is out.

As of 8 p.m. Sunday, the blaze could be seen for some distance. Traffic was also backed up in both directions into New Jersey and Pennsylvania along Interstate 80, which goes through the water gap at the base of the mountain.

Sandt said the cause of the fire is undetermined but said the weather is likely not a cause. Open fires are not permitted in either the state forest or the national recreation area.

The lack of snow cover and relatively dry conditions the area has seen this winter could be conducive to a greater risk of fire catching and spreading.

Sarah Johnson, a National Weather Service meteorologist, said the region is not currently in a drought monitoring situation, but precipitation this winter has been less than normal.

At the NWS's reporting station in Mount Pocono, Pa., the nearest to the Delaware Water Gap for which precipitation data are available, Johnson said 1.43 inches of rain have fallen so far this month —about a half-inch below normal for this time of February. Going back to Dec. 1, Mount Pocono has received 6.13 inches of rain, about 2.5 inches below normal.

Further updates on the fire can be found on the Delaware Water Gap National Recreation Area's Facebook page.

New Jersey Herald reporter Eric Obernauer contributed to this story.