A wildfire in South Jersey’s Wharton State Forest spread to 12,000 acres Monday, as officials said it was on track to become the largest wildfire in the state in 15 years.

First spotted Sunday morning along a remote section of the Mullica River, and fueled by dry and breezy forest conditions, the blaze quickly reached townships in Gloucester, Burlington, and Atlantic Counties. No injures have been reported.

The fire, 70% contained as of Monday afternoon, is expected to be completely under control later this week — but could consume about 15,000 acres before then, New Jersey Forest Fire Service Chief Greg McLaughlin said at a news briefing Monday afternoon.

The cause of the fire remains under investigation, but McLaughlin said officials have ruled out natural causes.

“The majority of our forest fires are human caused and it’s important to recognize that because it places it within our power to avoid circumstances like this,” said Shawn LaTourette, commissioner of the New Jersey Department of Environmental Protection.

McLaughlin said there was “really extreme fire intensity” throughout the day Sunday due to dry conditions and high winds. The fire moved back and forth across the Mullica River. Firefighters were unable to make a direct attack on the fire and instead had to start backfires to burn vegetation around the perimeter.

“The fire moved in different directions. It spread quickly and with high intensity,” McLaughlin said.

Officials shut down the Mullica River Campground, its trail, and related water activities, such as boating. Pinelands Adventures suspended all its canoe and kayak operations and by late Sunday night, the Paradise Lakes Campground had been evacuated.

There were 18 structures threatened by the fire, McLaughlin said, at state and private campgrounds and several farms, including blueberry and cranberry farms. Firefighters have created barriers with backfires around those structures to protect them.

By Monday, authorities shut down sections of Routes 206 and 542.

Batsto Village and all its trails, the Atsion Recreation Area, and the Lower Forde Campground were all added to the list of closures.

McLaughlin said there wasn’t any threat as of Monday afternoon that residential areas would need to be evacuated.

The smell of smoke from the fire traveled as far as the Jersey Shore, reaching Ventnor and Ocean City.

Local volunteer fire departments from Atlantic, Burlington, and Ocean Counties have been providing protection to the 18 structures threatened by the fire.

Fire authorities said they would continue with backfire operations to contain the fire and asked the public to steer clear and not fly drones in the area.

McLaughlin said the fire could be mostly contained by late Monday night, and he expected it could be 100% contained Tuesday or Wednesday, depending on whether it rains.

Staff writers Amy S. Rosenberg and Kasturi Pananjady contributed to this article.