A woman attacked seven people with a substance like pepper spray in four places in Harlem and the Upper West Side on Friday, including two subway stations, in a series of attacks that were being investigated as possible hate crimes, the police said.

Detective George Tsourovakas, a police spokesman, said the woman was black and the seven victims were white. He declined to elaborate on the hate crime investigation.

As of Friday night, the police were still searching for the woman, who had not been identified or arrested.