A 99-year-old woman was sexually assaulted and beaten up in this Australian city by a man, suspected to be in his teens or early 20s, who forced his way into her home, police said.

The sex attack took place last week when the old woman was alone at her home in Koornang Road, Ormond, The Age reported Friday.

A man, who the police suspect is in the age group between 17 and 22, knocked on her door and then forced his way inside between 10.30 a.m. and 11 a.m.

The attacker then physically and sexually assaulted her for up to half an hour. He then fled from the spot.

Detective Inspector Glenn Davies of the Sexual Crimes Squad said the attack had a 'profound effect on the woman and her family'.

'We're very concerned about this type of crime ... This woman is a grandmother, and a great-grandmother. I think people in the community would be absolutely appalled by this,' Davies was quoted as saying.

He said the assault left the victim 'very traumatised' and she was in hospital for almost a week.

The woman who was pushing 100 received cuts around her face and cuts on her legs, and she was struck on the head with an object.

Davies said: 'Obviously this callous disregard for this person is a concern to us. The person may have been loitering or stalking in the area before the attack occurred.'