Hundreds of protesters closed a major Chicago intersection Tuesday night after authorities released a "disturbing" dashcam video of the moment a cop shot 17-year-old Laquan McDonald 16 times last year.

Chicago police Officer Jason Van Dyke, 37, turned himself in Tuesday and was ordered held without bond on a charge of first-degree murder in Laquan's death in October 2014.

City and state police walked alongside demonstrators, who largely remained peaceful as they clogged the intersection of Roosevelt Road and Michigan Avenue in the South Loop. The protest started when 30 to 40 people met in an art gallery after City Hall released the graphic video, saying they were there to reflect and to discuss their emotions.

NBC Chicago: Protesters March After Release of Laquan McDonald Video

As more people joined, they marched about a block to Roosevelt Road, chanting "16 shots!" and "Is this a joke? They think it's a joke!"

"If we want young people to believe in the system, the system has got to work," said Michael Pfleger, senior pastor of St. Sabina Church and a prominent Chicago activist.

Protesters remained on the streets at 1:30 a.m. local time (2:30 a.m. ET) but police declined to comment on whether arrests had been made.

Even before they made the video public, Mayor Rahm Emanuel and Police Chief Garry McCarthy were braced for protests, pleading for calm at a late-afternoon news conference.

"Anyone who is there to uphold the law cannot act as though they are above the law," Emanuel said. "Jason Van Dyke does not represent the police department."

Noting that Laquan's family had also urged a peaceful reaction, Emanuel asked: "Will we use this episode in this moment to build bridges, or will we allow this episode to tear us apart?"

The six-minute, 53-second video has no audio — police said none was ever recorded.

About five minutes, 20 seconds in, it shows a young man, later identified as Laquan, walking down the middle of a street as multiple officers draw their weapons. One of the officers appears to fire his weapon, and the man spins and collapses on his right side.

His body continues to jerk as more shots apparently are fired into him; then an officer walks up and kicks something out his hand. Police have said Laquan was carrying a 3-inch-long knife.

Chicago police Officer Jason Van Dyke. Cook County, Illinois, State's Attorney's Office

McCarthy said he had been expecting — and dreading — this day for a long time.

"People have a right to be angry, people have a right to protest, people have a right to free speech, but they do not have a right to commit criminal acts," McCarthy said.

"Every day in this city, you see thousands of officers performing admirably," he said. "The officer in this case took a young man's life, and he's going to have to account for his actions."

The Chicago public school system deemed the video so disturbing that it sent pupils home with a letter to parents Tuesday saying counselors would be available, NBC Chicago reported.

Demonstrators hold hands to block an intersection as police keep watch during protests Tuesday night in Chicago. Jim Young — Reuters

Prosecutors said Tuesday that Van Dyke emptied his gun and prepared to reload, but lawyers for Van Dyke have said the shooting was justified because he felt threatened.

Prosecutors said in court, however, that the video "clearly does not show McDonald advancing" on the officer. Laquan, they said, was on the ground for 13 of the 15 seconds Van Dyke repeatedly fired.

Photos: Laquan McDonald Police Shooting Video Ignites Chicago Protests

McDonald was wounded in his scalp, neck, left chest, right chest, left elbow, left forearm, right upper arm, right hand, right upper leg, left upper back and right lower back.

"It is graphic. It is violent. It is chilling," Cook County State's Attorney Anita Alvarez told reporters after Van Dyke's hearing. "This video will tear at the hearts of all Chicagoans."

Laquan McDonald in a family photo. NBC Chicago

Alvarez said that Van Dyke was at the scene for less than 30 seconds before he started shooting and that he opened fire only six seconds after he got out of his car. Of the eight officers at the scene, Van Dyke was the only one to open fire, she said.

Dan Herbert, an attorney for Van Dyke, agreed that the video is "difficult to watch," but he said it doesn't clarify whether Van Dyke acted inappropriately in shooting Laquan, who an autopsy showed had PCP, or angel dust, in his system.

Many questions have been raised about why prosecutors took 13 months to bring charges — and about whether the police department has tried to bury the incident.

NBC Chicago quoted a district manager for Burger King in May as saying Chicago police deleted separate video from a security camera at a Burger King restaurant less than 100 yards away,

While 86 minutes of the video were missing, the city's Independent Police Review Authority said there was "no credible evidence" that police tampered with it. Alvarez repeated that assertion Tuesday.

The City of Chicago has paid Laquan's family $5 million. Van Dyke was placed on "no-pay" status.