A middle-aged Indian woman attacked her alleged stalker and cut off his genitals before rushing him to hospital to save his life, police said on Thursday.

The accused woman on Tuesday asked two men to lure the 25-year-old to an isolated place in the suburbs of Mumbai where the three of them assaulted him and the woman used a kitchen knife to cut off his genitals, police said.

In a statement to police, the 42-year-old woman said the victim was her neighbour and had several times harassed her. She decided to "teach him a lesson", a police inspector told Reuters.

But the woman realised he could die and rushed him to hospital. Both the knife and the genitals have been recovered, police said.

"He is on ventilator support and is still critical," said a doctor at the hospital.

The woman and her two alleged acquaintances are in police custody while investigations continue.

Sexual violence and harassment of women have been a growing concern in India in recent years and police and governments have been criticised for failing to keep the streets of major cities safe.