Toronto police have released security images of a suspect after a sexual assault on a TTC subway train.

Just after 10:30 a.m. Tuesday, a 21-year-old woman was heading west on Line 2.

When the train stopped at Woodbine Station, a man boarded and reportedly sat beside her.

He then allegedly committed an indecent act, grabbed the woman and sexually assaulted her.

The suspect then got off the train when it stopped at Greenwood Station and fled on foot.

He is in his late teens to early 20s, five feet five inches tall, with a thin build, short brown or black hair, and clean-shaven. He was wearing a black hooded jacket, a grey top with a burgundy hood, black pants with a white stripe down the side and running shoes.