Police used tear gas and water cannons on protesters near Standing Rock demonstrating against the Dakota Access Pipeline on Sunday night (local time).
The clashes took place on a bridge north of the camps set up by demonstrators in opposition to the pipeline.
At least one person was reportedly arrested, and 167 people were injured, an Indigenous Environmental Network spokesperson told The Guardian.
Concerns of hypothermia were raised after police used water cannons on protesters as temperatures dipped below freezing.
"As medical professionals, we are concerned for the real risk of loss of life due to severe hypothermia under these conditions," said the Standing Rock Medic and Healer Council in a statement on Facebook.
The Morton County Sheriff's Department estimated the number of protesters to be 400.
The Dakota Access Pipeline is being constructed to carry oil from western North Dakota to a refinery in Illinois. The local Standing Rock Sioux tribe says the pipeline will threaten their sacred native lands, and contaminate their water supply from the Missouri River.