The fire was reported Sunday afternoon in Hardwick Township's Worthington State Forest off Mount Tammany's Red Dot Trail, and could be seen from Route 80.
The mountain peak overlooks the New Jersey and Pennsylvania border on Route 80.
Hikers on Sunday were allowed to descend on the Blue Blazed and Red Dot trails but access was closed to visitors on their way up.
The fire remained active as of 10 a.m. Monday morning. The cause remains under investigation but "did not begin as a controlled or prescribed burn," according to the National Park Service.
New Jersey blog NJ Spots launched a donation page for the National Park Service and local firefighters who responded. That campaign had raised more than $200 as of Monday morning.
Hikers that frequent the trail crafted posts on social media wishing for the best.
A Route 80 motorist posted videos of the blaze Sunday night.
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