Update, 9:45 p.m.

At least 48 people were arrested on Sunday for obstruction of a public passageway during the hostile Alton Sterling protest in downtown Baton Rouge, officials said.

Update, 8 p.m.

A march from Wesley United Methodist Church to the State Capitol Sunday protesting the death of Alton Sterling at the hands of Baton Rouge police went from peaceful to confrontational when protesters decided to continue walking on Government Street to the Police Department’s Headquarters.

At least 12 people had been arrested by early evening while hundreds of demonstrators were locked in a standoff with law enforcement at the corner of East Boulevard and Government Street, which grew in intensity as the planned protest was originally expected to die down.

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Baton Rouge police spokesman Sgt. Don Coppola said the problem began when protesters tried to go off the pre-approved route — from the church to the Capitol —— and instead headed both on to Government Street and toward Interstate 10 to block it.

Coppola said the police felt protesters were going to I-10 via France Street but they never actually got on an interstate ramp.

Baton Rouge police officers along with SWAT team members and Louisiana State Police made a dramatic appearance when dozens of officers marched down the road behind an armored police vehicle, which pushed the crowd back, and ordered the protesters, who were gathering on private property and clogging public roads, to disperse.

At one point the slow moving armored vehicle was pushing up against the bodies of protestors, who linked their arms together.

The police officers were decked out in full riot gear, initially wearing gas masks with some holding assault rifles, which only led to chants from excited protestors that the police were inciting the violence.

For several minutes the armored vehicle let out a high-intensity siren. The siren they used is called an “El Rad,” police said. Protesters said it was so loud that it hurt their ears. Police said the siren is intended to disperse crowds and that Sunday was the first time it was ever used in Baton Rouge.

At least 12 people had been arrested by 7 p.m. Sunday, with some of the protesters violently thrown on the ground.

After several minutes of conflict, officers lined up on one side of East Boulevard with protestors on the other side. The officers all removed their gas masks, as if to calm the threat of shooting tear gas canisters at the crowd.

Protesters chanted, “You are not your uniform,” “Black Lives Matter,” and “No Justice, no peace,” as the night went on. Police spokesman Lt. Jonny Dunnam said he suspected the people leading protestors into the evening were no longer the organizers of the original demonstration.

“Go ask them, none of them are from here,” he said.

The march was initiated by the NAACP of LSU and other young activist groups. It had been peaceful and law enforcement remained at bay as protesters marched from the church to the State Capitol and back to the church. The confrontation began when protesters decided they wanted to continue marching.

By 7:30 p.m. the East Baton Rouge Parish Sheriff’s Office SWAT team, also in riot gear, created another barrier for the protestors. Law enforcement from three different sides started marching inward toward the crowd of protestors, encircling them and instructing them to disperse or be arrested.

It led to another round of confrontations and arrests. It was unclear how many more arrests were made during that round than the 12 who were arrested earlier in the evening.