More than a dozen protesters were arrested as tense standoffs with police broke out during a march across the Brooklyn Bridge that began in Union Square.
Tuesday's protest marked one of the first major demonstrations since two officers were fatally shot in Bedford-Stuyvesant in December.
Rallying to the names of those killed by police, the mobs of protesters marched down Broadway towards the Brooklyn Bridge, which led to several tense interactions with NYPD officers following the crowd.
Hundreds of picket signs were raised among the crowds, with messages reading, "The whole system is guilty," "Stop murder by police," "Ferguson is everywhere!" among others.
At one point protesters crossed the Brooklyn Bridge, blocking traffic. During the protest police said at least one NYPD sergeant was punched in the head and shoulder. He was taken to an area hospital. No one had been arrested for the incident as of late Tuesday evening, police said.
Mayor Bill de Blasio called the attack "unacceptable" and said it "will absolutely not be tolerated." In a statement on Tuesday evening, de Blasio said the attack, as well as a potential second attack, will be investigated.
"And any other person who might use the right to peaceful protest as cover to initiate violence, cause mayhem or incite disorder – whether against the police, the people or property of our great City – should consider themselves on notice that New York City will not stand for it," de Blasio said in the statement. "Anyone who decides foolishly to engage in such destructive acts can expect a swift arrest and aggressive prosecution. As I have said before, such activity is beneath the dignity of New York City."
An exact number of arrests was not immediately available.
The group staged several die-ins, including near the Atlantic Center, where dozens laid down in the street -- a form of protest that gained traction in the aftermath of Michael Brown being fatally shot by a police officer in Ferguson, Missouri.
They stopped traffic in the intersection of Broadway and Houston Street as well as Broadway and Canal Street, chanting "I can't breathe" and "whose streets, our streets."
Dan Lowe, an artist from Brooklyn, said that it was important for people of all color, age, background to be part of the protest and support the people's injustices.
"As somebody who's not a person of color and who doesn't really get affected by this, I felt it was still important to say black lives matter," Lowe, 31, said. "We need to show that we as a people are united around this common goal of justice for anybody and everybody, no matter where they are or who they are."
Tuesday's protest follows the April 4 shooting of Walter Scott, an unarmed black man who was killed by wite police officer Michael Slager in North Charleston, South Carolina.
Among those leading the group included activist Dr. Cornel West and Nicholas Heyward, the father of Nicholas Heyward Jr., 13, who was shot dead by police in Brooklyn public housing while playing cops and robbers with a toy gun.
"I have been protesting with a lot of the parents, a lot of which are standing behind me. They have innocent children that were murdered in New York City," Heyward said. "We shouldn't be out here today. Our ancestors already fought and died for the things we're fighting for right now. We need to organize ourselves together to put an end to this."
The protesters tensely faced off with police on the corner of Worth Street, but weaved around and headed towards the plaza near police headquarters. While police tried to stop the protesters from moving further, they fought their way onto the Brooklyn-bound side of the Brooklyn Bridge.
Several dozen uniformed officers then came up from behind, allowing traffic to proceed. The group continued along the pedestrian path, shouting at the stationed officers below, "Who do you protect? Who do you serve?"
The group advanced onto Adams Street in Brooklyn, and a couple dozen people laid down. After several more arrests, the protesters weaved their way through the streets of Brooklyn, blocking traffic on Flatbush Avenue, and marching into Park Slope. They blocked the rush hour traffic by the intersection of Atlantic and Flatbush avenues, near the Barclays Center.
More arrests were made later Tuesday at Flatbush Avenue and Sterling Place.
West, a prominent activist and scholar, rallied the importance of the protest for black people of all generations.
"Sojourner Truth ain't no joke. Martin Luther King ain't no joke. We're here because we love those folk," West said. "And when you love the folk, you tell the truth and you stand up for them. We want the police accountable."
Similar protests broke out in the following the acquittal in the Michael Brown case and the decision by a grand jury to not indict a police officer in the death of Eric Garner, the Staten Island man who died after being placed in an apparent chokehold while being arrested.
Pattie Briggs, a mother from Jamaica, Queens, said that something must be done soon to end the fatal shootings by police officers.
"It's so heartbreaking to see all these deaths. I have a son and I don't want him to be one of these victims," Briggs, 53, said. "We have to let the cops and everyone know how we feel about this. It shouldn't just be you kill a black man and it's over."