The blaze in the Wharton State Forest was reported early Friday. Officials believe it began in the area of the Batona Campground in Tabernacle, which was evacuated as a precaution.

The New Jersey Forest Fire Service said Saturday that the blaze has now burned an estimated 4000 acres (1618.74 hectares), but they report having made “substantial progress” in containing the fire. Officials said crews were monitoring and improving containment lines and conducting burnout operations in pockets of unburnt fuel, US News reported.

Officials said earlier that crews were using a backfire operation to help combat the blaze, which involves burning areas ahead of the main fire in a bid to stop the flames from spreading. Several roads and trails have been closed, US News reported.

The cause of the fire remains under investigation.