(CNN) Police and about 400 people who were protesting the Dakota Access Pipeline clashed Sunday evening as demonstrators set fires and law enforcement officers fired rubber bullets, tear gas and water at the crowds, authorities said.

A live stream from the site near Cannon Ball, North Dakota, showed a chaotic, loud scene, with people screaming and car horns honking. a

Protesters were attempting to cross the Backwater Bridge and go north on Highway 1806, according to the Morton County Sheriff's Department, which described Sunday's events as a riot.

An estimated 400 protesters attempted to cross the bridge to go north on highway 1806.

Protesters set a dozen fires near the bridge, police said. On Sunday night, police released a statement saying that the protesters "attempted to flank and attack the law enforcement line from the west," describing their actions as "very aggressive."

Officers tried to disperse the crowds with water sprayed from hoses attached to fire engines, and also fired rubber bullets and tear gas, Morton County Sheriff's Department spokeswoman Maxine Herr said.

Some protesters were taken to a hospital after being hit by rubber bullets, said Dallas Goldtooth, an organizer with the advocacy coalition Indigenous Environmental Network

The sheriff's department did not say how many protesters were injured, but said an officer was in fair condition after being hit in the head by a rock. One person was arrested, police said.

An 11-minute aerial video posted online by a production business called Digital Smoke Signals shows someone spraying water at and around a few protesters who were standing near a line of law enforcement personnel. It also briefly shows water being sprayed at a fire.

Law officers were there to keep protesters from crossing the bridge, which the sheriff's department said was closed for safety reasons "due to damage caused after protesters set numerous fires" on it in a separate incident on October 27

The officers also are trying to keep protesters from trespassing on U.S. Army Corps of Engineers land to the north, the department said.

'Chaotic, dark, freezing'

Some decried the use of water on the crowd on a cold night when temperatures fell to 28 degrees Fahrenheit.

Dakota Access Pipeline protest standoff escalated Sunday evening.

"It was chaotic, dark, freezing," Indigenous Environmental Network spokeswoman Jade Begay said.

The coalition said protesters on Sunday were trying to remove one of two vehicles -- both burned in the October 27 incident -- from the bridge when authorities started firing the rubber bullets, tear gas and water.

The bridge's closure and the burned vehicles blocking it endanger residents to the south because it hinders easy access for any emergency vehicles coming from the north, the coalition says.

Begay said she arrived at the bridge for a peaceful demonstration at about 6 p.m. Sunday, and the water and rubber bullets started about an hour later.

"Every time I went out it felt really unsafe," Begay said. "It was all commotion, very chaotic. All this chaos (was) caused by the police and their law enforcement putting out the noise cannons, spraying people with water."

Begay said authorities have been preventing protesters from crossing the bridge to "lock us in." A camp of protesters lies south of the bridge.

Physicians and tribal healers with the Standing Rock Medic and Healer Council called for "the immediate cessation of use of water cannons" over concerns of hypothermia in the cold weather conditions. They criticized the "potentially lethal use of these confrontational methods against people peacefully assembled."

But police say some of the protesters were not peaceful and that water was used to put out fires as well as to control the crowds.

"There are multiple fires being set by protesters on the bridge and in the area of the bridge," said Donnell Hushka, another spokeswoman for the Morton County Sheriff's Department. "We have fire trucks on the scene (and) they are using their fire hoses to put out the fires, wet the land around so fires don't spread and they are also using water as crowd control."

Begay said there were "peaceful bonfires" around which protesters were gathering to keep warm. The coalition alleged that other fires were grass fires ignited by flares shot by law enforcement.

"They don't need to be meeting us with Mace and rubber bullets when we are nonviolent. There is no form of aggression or violence," she said.

Protests have simmered for months, spawning bitter clashes over the 1,172-mile oil pipeline that would span from North Dakota to Illinois.

Why protests are happening

Protesters say the Dakota Access Pipeline will threaten the environment and destroy Native American burial sites, prayer sites and culturally significant artifacts. The Standing Rock Sioux Tribe says construction of the pipeline -- which is currently slated to run under the Missouri River -- could affect its drinking water supply and put communities living downstream "at risk for contamination by crude oil leaks and spills."

Multiple groups have joined the protests over the months. Activists have destroyed construction equipment as part of their protests.

Protesters appear to be digging in their heels for the winter by building structures in a protest camp without permits, the Morton County Sheriff's Department said.

"Their actions are both illegal and likely insufficient to protect them from the elements," Morton County Sheriff Kyle Kirchmeier said. "We've seen that many of these protesters are not from North Dakota and may not be familiar with the harshness of our winters, and we urge them to leave the camps and seek appropriate shelter for their own health and safety."

Bernie Sanders tweeted that the president "must protect the safety of Native Americans and their supporters who have gathered peacefully to oppose the Dakota Access Pipeline."

.@POTUS must protect the safety of Native Americans and their supporters who have gathered peacefully to oppose the Dakota Access Pipeline. https://t.co/dgNOwwvhLw — Bernie Sanders (@SenSanders) November 21, 2016

More than 525 people have been arrested in connection with the protests since they began months ago, the Morton County Sheriff's Department said Monday.

Status of the pipeline

Energy Transfer Partners and Sunoco Logistics Partners took legal action, asking a federal court to allow them to complete the pipeline.

Dakota Access is a $3.7-billion project that backers have touted as the safest and most efficient way to transport oil, rather than using rail or trucks.