Campers set structures on fire in preparation of the Army Corp's 2pm deadline to leave the Oceti Sakowin protest camp on February 22, 2017 in Cannon Ball, North Dakota. Activists and protesters have occupied the Standing Rock Sioux reservation for months in opposition to the completion of the Dakota Access Pipeline. (Photo by Stephen Yang/Getty Images)

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CANNON BALL, N.D. (CBSMiami/AP) — A SWAT vehicle is ready for use if force becomes necessary to remove the remaining protesters from the now-closed Dakota Access pipeline protest camp on federal land in North Dakota, authorities said Thursday.

American Indian elders have told police there are people willing to resort to drastic measures to stay in the camp that was shut down Wednesday ahead of spring flooding, Highway Patrol Lt. Tom Iverson said. Similar sentiments have been expressed by protesters on social media, Iverson said.

Authorities are prepared for a worst-case “SWAT scenario” should anyone who is armed barricade themselves in a structure in the camp, Iverson said. A Special Weapons and Tactics vehicle was at the scene.

“We’re doing everything we can to avoid that kind of a situation,” he said. “We don’t want it to reach a flash point, but at some point, enough is enough.”

The camp — known as Oceti Sakowin — near the Standing Rock Indian Reservation has since August been the main site for demonstrators trying to thwart construction of the final section of the $3.8 billion pipeline. The Standing Rock Sioux and Cheyenne River Sioux, whose reservation is downstream, say Dakota Access threatens their drinking water and cultural sites. Texas-based Pipeline developer Energy Transfer Partners disputes that.

When complete, the project will carry oil through the Dakotas and Iowa to a shipping point in Illinois.

At its peak, the camp was home to thousands of protesters. Of the few hundred who remained Wednesday, most marched out of the area ahead of the 2 p.m. deadline imposed by the Army Corps of Engineers. Authorities arrested 10 people who defied the order in a final show of dissent.

Gov. Doug Burgum estimated Wednesday night that as many as 50 people remained in the camp. Police early Thursday said another 15 had crossed a frozen river and entered the camp on foot.

Burgum has said those remaining at the camp can still leave without facing charges. The state planned to send a bus to the site at midday to transport anyone to Bismarck, where officials were doling out basic necessities, along with hotel and bus vouchers.

Protester Ed Higgins, 39, of Lowell, Massachusetts, said by phone from the camp, that Lakota elders want to meet law enforcement to state their belief that the camp is on land that rightfully belongs to Native Americans.

“They don’t have any right to come in here,” he said of police.

Corps Col. John Henderson has said the taxpayer-funded cleanup of the site could take about a month and cost as much as $1.2 million. The Corps had warned that the protesters need to leave the site before the spring melt floods the land and spreads debris from the camp downriver.

Early Wednesday, protesters burned some wooden structures on site in what they described as a leaving ceremony. Authorities said about 20 fires were set and a 7-year-old boy and a 17-year-old girl were taken to hospitals to be treated for burns.

Shortly before the deadline passed, about 150 people marched out of the soggy camp, singing and playing drums as they walked down a highway, carrying an American flag hung upside-down.

(TM and © Copyright 2017 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2017 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)