CANNON BALL, N.D. — Police in armored vehicles and donning riot gear clashed with activists as demonstrations against a controversial North Dakota oil pipeline reached a new peak early Friday.

Authorities had arrested 141 protesters by midnight (1 a.m. ET), culminating a more than six-hour standoff over the stretch of private land lying in the pipeline's path, the Morton County Sheriff's Department said in a statement.

The scene at the Cannonball Ranch, located near the capital city of Bismarck, devolved into chaos throughout Thursday.

Demonstrators blockaded roads and bridges by setting fire to bales of hay and construction equipment. The sheriff's department said at least seven protesters used "sleeping dragon" devices, which typically involve PVC or other pipe, to physically latch themselves onto vehicles and large concrete. According to police, some protesters threw rocks and improvised fire bombs as law enforcement officers closed in.

One woman fired three shots from a revolver at police, an emergency services official said. No one was hit.

Police forces responded by using pepper spray and firing bean bags on protesters. They used a long-range acoustic device with a high-pitched tone to disperse the crowd. Meanwhile, Humvees and buses roamed the scene as two helicopters and an airplane scanned the operation from the air.

Authorities said an escalation from activists who were building encampments on private land, left them no choice but to intervene.

"We're trying to avoid confrontation. But they drew the line in the sand today," Cass County Sheriff Paul D. Laney told reporters Thursday.

The chairman of the Standing Rock Sioux Tribe criticized law enforcement's "militarized" response to the camp and called for demonstrations to remain peaceful, but stressed that activists would not give up their cause.

"We won't step down from this fight. As peoples of this earth, we all need water. This is about our water, our rights, and our dignity as human beings," Dave Archambault II said in a statement Thursday evening.

Protesters on horseback galloped toward the law enforcement line before wheeling around and some had begun throwing objects at the officers, North Dakota State Emergency Services Spokeswoman Cecily Fong told NBC News.

"They've definitely escalated, they're throwing rocks and debris," she said, adding that a handful of officers suffered minor injuries.

The protesters, comprised of a group that includes Native Americans and environmental activists, had been camped on private property since Sunday near the $3.8 billion Dakota Access Pipeline, near the town of Cannon Ball.

The 1,172-mile pipeline would run within a half-mile of the Standing Rock Sioux reservation. Opponents of the project say the pipeline could adversely impact drinking water and would disturb sacred burial sites.

Demonstrations at the site have garnered widespread national attention, attracting celebrities and prominent activists to join the cause.

Democratic presidential nominee Hillary Clinton's campaign weighed in on the protests Thursday evening.

"Now, all of the parties involved — including the federal government, the pipeline company and contractors, the state of North Dakota, and the tribes — need to find a path forward that serves the broadest public interest," spokeswoman Xochitl Hinojosa said in a statement.

Hundreds of protesters from Standing Rock and other tribes have set up camp for months in protest a few miles away from where Thursday's confrontation occurred, close to where the Missouri and Cannonball rivers meet.

The protesters had created a camp in the pipeline's path on private property known as the Cannonball Ranch on the side of the highway and set up the roadblocks along on Sunday.

Highway 1806 remained closed Thursday between Fort Rice and Cannon Ball, according to the sheriff department's statement. Various counties, cities, state agencies and out-of-state law enforcement were helping the Morton County Sheriff's Department, the statement said.

"There's no fear here," one protester told NBC News. "We know that we have the moral high ground and that we're doing what is right, not only for the human race, but for the rights of nature."