In one of the most heinous crimes, a 99-year-old woman was sexually assaulted in her home in southeast Melbourne.

The horrendous attack occurred when the woman was alone in her home in Koornang Road, Ormond.

A Victoria Police spokeswoman said a man, thought to be aged between 17 and 20, knocked on the woman's door and forced his way inside and thereafter, physically and sexually assaulted her before fleeing on foot, reports The Age.

Paramedics treated the woman at her home before taking her to hospital.

Police has already released an image of the wanted young man and will set up an information caravan on Koornang Road. (ANI)