A woman drove her car into a crowd of protesters on 39th Street and 3rd Avenue in Manhattan just after 4 p.m. on Friday, injuring at least six people, the police said.

A video posted on Twitter shortly after the incident showed protesters standing close to a black BMW sedan on Third Avenue, with at least one of them slapping its windows.

The car surged forward, flinging protesters to the ground, then sped through an intersection, striking more pedestrians, some on bicycles, with a sickening crunch, the video shows.

Sofia Vickerman, 18, a freshman at New York University, said she was in the middle of the pack of protesters when she heard screams coming from the front. “Bodies were in the air and bikes were flying,” she said.

None of the people hit by the car were critically injured, and the driver’s intentions were unclear, the police said. The driver was being detained by the police but it was not known whether she would face charges.

Another video posted online by a bystander showed a redheaded woman wearing what appeared to be a sweatsuit being taken into custody by the police as protesters shouted at her from the sidewalk.

The protesters were marching in support of Immigration and Customs Enforcement detainees on a hunger strike, according to a Twitter account that provides updates on protests in the city.

Ms. Vickerman said the protest had started in Times Square and had made its way downtown, with police trailing on bicycles. She then saw the car driving through the crowd of protesters. She said she did not hear or see the motorist show any signs of aggression before hitting the protesters.

This breaking story will be updated as more information becomes available.