The victims, all in their 30s, were stabbed on the N, D and R platform of the 36th Street station, at Fourth Avenue in Sunset Park, around 5:20 a.m., authorities said.
They were taken to NYU Langone Hospital—Brooklyn.
Two of them suffered minor injuries, according to the FDNY. The condition of the third victim was not immediately clear.
The circumstances leading up to the stabbing were also unclear Wednesday morning.