Toronto police are asking for help identifying a suspect after a 24-year-old woman was sexually assaulted in the city's Willowdale neighbourhood early Thursday morning.

Police said a 24-year-old woman was walking in the area of Yonge Street and Empress Avenue when a man approached her and asked a question.

The man allegedly then sexually assaulted the woman. When she tried to get away, police said, the suspect followed her.

The woman walked into a nearby building, where she approached security, police said. The suspect then fled the area.

On Thursday, police released security camera images of the suspect, who they described as five-foot-11 with a skinny build.

He was wearing a grey vest, black jacket, white T-shirt, black beanie hat, a backpack, and low-rise Doc Marten boots. His face was covered with a white cloth.

Police are asking anyone with information to contact them at 416-808-7474 or Crime Stoppers anonymously at 416-222-TIPS (8477).