Toronto police are alerting the public after a woman was followed and sexually assaulted by a man in an Etobicoke parking lot last week.

Police said the attack occurred in a lot in the 5400 block of Dundas Street West, just west of Shorncliffe Road, on Friday at 10:25 p.m.

The 46-year-old woman was walking east on south sidewalk of Dundas when a man approached from behind and began yelling at her.

She turned around and walked through the parking lot, but the man followed her and sexually assaulted her, police said Monday.

The suspect fled when a bystander came to the woman's aid, police said.

No one has been arrested.

Police said the male suspect is white, in his 30s and about six feet tall with a medium build. He was wearing blue jeans and a dark jacket.

Anyone with information about the suspect or the incident is asked to call police at 416-808-2200 or Crime Stoppers anonymously at 416-222-8477.

Investigators also want to speak to the person who came to the woman's aid.