It was not clear why the demonstrators were being detained and if they were being charged.
A small crowd of demonstrators and onlookers jeered police and attempted to block at least one van that was transporting a group of detained protesters.
Late Thursday, police shut down the 1900 block of 18th Street after officers corralled a group of demonstrators on a sidewalk.
Earlier in the evening, a police spokesman said officers had been following marchers, a standard response to facilitate what police deem as peaceful demonstrations and marches.
As protesters were surrounded by officers, some people viewed camera phone footage that appeared to depict police shoving some protesters to the ground as officers moved on the group.
Some marchers who were not corralled said that police used batons and pepper spray on demonstrators as they boxed them in.
Tysean Hoffman, of Alexandria, said the group of marchers numbered about 50 and began to march from Meridian Hill Park (also known as Malcolm X Park) toward the Third District police station and throughout Northwest Washington.
Some marchers lit fireworks, turned over trash cans and may have lit at least one trash can on fire, Hoffman said. But there was no damage to property and the marchers were otherwise peaceful.
Hoffman said he joined the march to ensure his 7-year-old son could live without fear of police. “I want my son to see a police officer and not be scared,” he said.
Other marchers said there were about 20 demonstrators and legal observerswho were surrounded in the group.
One woman, who declined to give her name, narrowly avoided being taken into custody as one officer pushed her with a baton as police tried to secure the scene. The woman said a friend jumped between her and the officer. Several other police officers detained him and one officer used pepper spray on her as they arrested him, she said.
“All of a sudden, the police got aggressive with us,” the woman said as she used ice and water to try to soothe burning from the pepper spray deployment.