Toronto police say a woman was sexually assaulted after she stepped off a TTC bus in Etobicoke early Sunday morning.

Police said the woman exited a westbound bus on Bloor Street West at about 2 a.m. and walked north on Laurel Avenue, where a man approached her from behind and grabbed her.

The man indicated he had a knife but the woman did not see one, police said.

A witness interrupted the attack and the suspect fled south on Laurel Avenue.

He is 20 to 30 years old and six feet tall with a thin build and short black hair. He was wearing dark clothing.

Police are asking anyone with information to call police at 416-808-7474 or Crime Stoppers anonymously at 416-222-8477.