Steph Solis

USA TODAY

More than 20 protesters refusing to leave the Dakota Access pipeline camp were arrested Thursday after defying Gov. Doug Burgum's order to leave.

Most of the protesters left the encampment near Cannon Ball, N.D., by Wednesday’s deadline. Ten were arrested later that day and up to 50 remaining demonstrators were given until Thursday to leave.

Remnants of the camp went up in flames Wednesday when protesters set fire to wooden housing as part of a departure ceremony. About 20 fires were set and two people, a 7-year-old boy and a 17-year-old girl, suffered burns. Authorities said they were taken to a Bismarck hospital but didn't elaborate on their conditions.

"No matter what happens, we encourage everyone to remain peaceful and reiterate that our utmost concern at this time is the safety and well-being of all parties," the Standing Rock Sioux tribe said in a statement.

The encampment is on federal land between the Standing Rock Sioux Reservation and the pipeline route that the Dallas-based Energy Transfer Partners is constructing. Once complete, the $3.8 billion, 1,200-mile pipeline will carry oil through the Dakotas and Iowa to a shipping point in Illinois. The pipeline is almost complete, the stumbling block involving a controversial section that runs under North Dakota's Lake Oahe.

The tribe claims the pipeline threatens its drinking water and cultural sites. Legal efforts to block or further delay completion of the pipeline, led by the tribe and environmental groups, have been turned aside by the courts.

The protesters stayed on the federal land for six months. Hundreds of officers from several states were on hand to handle arrests, according to NBC News.

► Related: Judge denies request to halt Dakota Access pipeline work

The U.S. Army Corps of Engineers set the Wednesday deadline, citing the threat of spring flooding. About 150 people marched arm-in-arm out of the camp, singing and playing drums as they walked down a highway. One man carried an American flag hung upside-down.

Authorities sent buses to take protesters to the North Dakota capital of Bismarck, where they were offered fresh clothing, bus fare and food and hotel vouchers.

Some of the remaining protesters were focused on moving off federal land and away from the flood plain into other camps, said Phyllis Young, one of the camp leaders.

“The camps will continue,” she said. “Freedom is in our DNA, and we have no choice but to continue the struggle.”

► Related: Army to allow completion of Dakota Access oil pipeline

New camps are popping up on private land, including one the Cheyenne River Sioux set up about a mile from the main camp.

“A lot of our people want to be here and pray for our future,” tribal Chairman Harold Frazier said.

Charles Whalen, 50, an alcohol and drug counselor from Mille Lacs, Minn., said he and a group of about 20 people were not going to leave on their own and were willing to get arrested to prove their point.

“Passive resistance,” Whalen said. “We are not going to do anything negative. It’s about prayer.”

A massive effort to clean up the camp has been underway for weeks, first by protesters themselves and now with help from the Army Corps in removing debris.

Some vehicles and pedestrians struggled to get through the muck created by recent rain and snow, and cleanup efforts were suspended partly because camp officials did not want heavy equipment making the conditions worse.

Contributing: John Bacon, USA TODAY; Associated Press