The shocking incident took place on platform number 10 when Priyadarshini, along with her father and grandmother, was waiting to board a train to Maharashtra's Solapur to attend a marriage.
As her father Srinivas went to buy the tickets, a youth appeared and attacked the girl with the knife. Other passengers standing nearby caught hold of the youth, thrashed him before handing him over to railway police.
The victim was taken to government-run Gandhi Hospital, where she died while undergoing treatment.
Police identified the assailant as 21-year-old Karan Kumar, a resident of Chittoor district. He is an engineering student at a private college at Putturu in the same district.
Kumar told police that his girlfriend is HIV positive and his friends used to taunt him for this. Unable to bear the insult, the youth left his native town, boarded a train and reached Secunderabad.
Police were questioning the assailant and trying to know why he attacked the girl.