Tensions flared anew on the Dakota Access pipeline as protesters tried to push past a long-blocked bridge on a state highway only to be turned back by a line of law enforcement using a water cannon and tear gas.

Sunday's skirmishes in Cannonball, N.D., began around 6 p.m. after protesters  tried to remove a burned-out truck on what's known as the Backwater Bridge so that local traffic can move freely again.

The bridge is not far from the encampment where they've been for weeks as they demonstrate against the pipeline. The Morton County Sheriff's Department estimated 400 protesters sought to cross the bridge on state Highway 1806.

Standing Rock protest

Protesters say they started fires in order to keep warm in -4 C weather. A statement from the local sheriff said demonstrators were trying to outflank and 'attack' law enforcement barricades. (Unicorn Riot/Twitter)

A live stream early Monday showed a continued standoff, with large lights illuminating smoke wafting across the scene.

The sheriff's department said in a statement around 1 a.m. Monday that approximately 100 to 200 protesters were on the bridge or in the vicinity. It said law enforcement officers "had rocks thrown at them, burning logs and rocks shot from slingshots," and that one officer had been hit on the head by a thrown rock.

Standing Rock protest

'Just got shot in the hand and back with rubber bullets. Tear gas, sound canon, flash bangs, and water canon,' protester Aidoneus Bishop wrote on Facebook, where he posted this photo.

Supporter Leland Brenholt said at least four people suffered wounds from rubber bullets. He said other protesters were hit with canisters in the chest and legs.

One protester showed his swollen hand on social media and said he was among those struck by rubber bullets.

A man helping organize the protests said about 180 protesters were injured in the latest skirmish with police. Dallas Goldtooth with the Indigenous Environmental Network said at least 17 people were taken to hospitals.

'Excessive' force

He said police turned the water on people while temperatures were below freezing and called it "an excessive and potentially deadly use of force."

At least one person was arrested. Protesters said a gym in Cannon Ball was opened to aid demonstrators who were soaked and exposed to chemical irritants.

Rema Loeb told The Associated Press he was forced to retreat from the bridge because he feared being doused with water on the freezing night. Others, he said, needed medical treatment after being hit with tear gas.

"It's been just horrible," said the 83-year-old Loeb, who travelled from Massachusetts about two weeks ago to join the protests.

Nearby gym opened for protesters

The 1,900-kilometre, four-state pipeline is being built to carry oil from western North Dakota to a shipping point in Illinois. But construction of the $3.8-billion US pipeline has been protested for months by the Standing Rock Sioux, whose reservation lies near the pipeline route, and the tribe's allies, who fear a leak could contaminate their drinking water.

​Two months ago, tribe officials said construction crews had removed topsoil on burial and cultural sites along the path of the proposed pipeline.

Energy Transfer Partners has said no sites have been disturbed and that the pipeline will have safeguards against leaks, and is a safer method of transport for oil than rail or truck. The company has said the pipeline is largely complete except for the section under Lake Oahe.

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Protesters and police during a protest against plans to pass the Dakota Access pipeline near the Standing Rock reservation. (Stephanie Keith/Reuters)

The bridge lies near where protesters had set up camp on private property owned by the pipeline developer, Energy Transfer Partners, before they were forcibly removed by law enforcement Oct. 27. It's also about a mile from an uncompleted section under Lake Oahe, a Missouri River reservoir, where work has been on hold by order of federal agencies.

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Police release tear gas during the protest against efforts to approve the pipeline. (Stephanie Keith/Reuters)

Tara Houska, an organizer with Honor the Earth, told the Bismarck Tribune that the Cannon Ball gym was opened to aid people who had been doused with water or tear gas.

Phone calls to the sheriff's department late Sunday went to an answering machine.

On Friday, Kelcy Warren, the chief executive of Dallas-based Energy Transfer Partners, said the company is unwilling to reroute the pipeline.

With files from CBC News and Reuters