Police are searching for a suspect who allegedly sexually assaulted a 21-year-old woman in Toronto’s underground PATH system on Sunday.

At around 10 p.m., Toronto police said the victim walked into the PATH at Wellington Street West, near St. Andrew subway station.

Officers say the suspect was already in the PATH when he started to follow the woman.

The suspect struck up a conversation with the woman before he allegedly sexually assaulted her, police said.

The victim tried to run away, but police said a struggle ensued. The suspect allegedly continued to assault her until a passerby interrupted, prompting him to run away through the PATH.

Toronto police describe the suspect as 20 to 40 years old, between five-foot-eight and five-foot-10, with short black hair and a moustache. He was last seen wearing clear-framed glasses, a blue bucket hat, a blue-hooded jacket, dark coloured pants and was carrying a greenish-cream-coloured backpack with brown straps.

Anyone with information about the incident is asked to call police at 416-808-7474 or Crime Stoppers anonymously at 416-222-TIPS (8477).