Dozens of people were arrested on Monday night in Lower Manhattan as hundreds participated in a march on Martin Luther King’s Birthday organized by Black activist groups, according to the police and witnesses.

Videos posted online by witnesses and participants show New York Police Department officers with helmets, batons and zip ties trying to clear protesters who had gathered on the streets and sidewalks near City Hall. Some of the marchers went to the area after walking across the Brooklyn Bridge.

A spokesman for the department said dozens of arrests were made between 8 p.m. and 10 p.m. in the vicinity of Chambers and Centre Streets. According to some videos posted online, the police began arresting people after urging the crowd to disperse.

The episode came in the late hours of Martin Luther King’s Birthday, and just days after the New York State attorney general, Letitia James, sued the New York Police Department over its handling of protests this summer after the death of George Floyd.

Ms. James is seeking to have a court-appointed monitor installed to oversee the department’s policing tactics at protests. If successful, this monitor would join another monitor appointed in 2013 to oversee how the city implements changes to its stop-and-frisk policy.

One witness to Monday night’s events, Jordan Plaza of the Bronx, said a relatively small number of protesters had spilled off the sidewalks and into the street when the police announced that they were obstructing the road and would soon be arrested.

“They weren’t approaching the police in a violent manner,” Ms. Plaza, 20, said. “Police randomly surged.”

Ms. Plaza said she had stumbled upon the protest earlier in the night on the way to see friends and joined on a whim. She said she was startled by what she saw and contrasted the treatment of protesters in New York City with the treatment of those loyal to President Trump who rioted inside the U.S. Capitol two weeks ago.

“It baffles me because the Capitol building, they were able to get in,” Ms. Plaza said. “Here, they were protesting outside a courthouse.” (The New York County Surrogate’s Court is on Centre Street, as is the Tweed Courthouse, which houses the New York City Department of Education.)

Hani Bello, a 27-year-old from Brooklyn, belongs to FreeBlackRadicals, one of several groups that she said responded to that evening’s “call to action” to protest.

After a gathering outside Barclays Center at 5 p.m. that featured speakers who frequently invoked the Rev. Dr. Martin Luther King Jr., Ms. Bello said she and others walked onto the Brooklyn Bridge, which bikers with the protest closed off to vehicular traffic. At one point, the group broke into ballroom dancing and vogueing. Ms. Bello said it warmed her up and that she took off her gloves and scarf.

“It is a form of resilience, being on that bridge, taking it over,” Ms. Bello said. “To feel resilient is part of Black liberation.”

After the marchers crossed the Brooklyn Bridge, the police blocked the road leading from the bridge to City Hall Park, she said. “The park is for the public,” it was open for use, she said. “People have the right to voice their opinions on taxpayer-funded land.”

On Monday night, images of officers yanking individuals out of a crowd of protesters began circulating widely on social media, and echoed scenes from last summer, when Black Lives Matter demonstrators flooded the streets in New York and other cities. A number of those videos helped fuel the lawsuit by Ms. James, the state’s attorney general.

The lawsuit she filed in federal court in Manhattan is the first time that the state attorney general has sued a police department, according to Ms. James’s office.

“There was ample ability and opportunity for the city and N.Y.P.D. leadership to make important changes to the way that officers interact with peaceful protesters, but time and time again, they did not,” Ms. James said.