For several days, police denied that any women had filed complaints of the assaults.
However, after CCTV footage of an attack went viral on social media, police announced they had set up an inquiry.
In one video, a woman was seen being grabbed and dragged to a scooter by two men, while a group of bystanders looked on.
Alleged victims claim they were chased, groped, molested and robbed by mobs of men during the late night celebrations across the city.
The announcement followed a public outcry over comments by a local minister blaming the attacks in Bengaluru on "western dress".
Police officers have been sifting through footage from at least 45 CCTV cameras installed in the city centre, where hundreds had gathered to celebrate the new year.
One alleged victim told the BBC the men attacked many women.
"There was not a single face you could make out or who was doing it," she said.
"As soon as you turned you would be groped or grabbed. There were so many people there that you could not pinpoint who was doing it.
"I felt helpless. Although I have hands and legs and I could abuse and slap them, I could not do anything. I didn't know who was touching me and groping me."
India has been shamed in the past by shocking levels of sexual assault against women.
In December 2012 there was an international outcry after a student was gang-raped on a bus in New Delhi and later died of her injuries.
