Toronto police have released security images and video of a suspect being sought in a brutal downtown sex assault.

Police say a woman was walking in the McGill Parkette near Gerrard and Yonge streets at around 2:30 a.m. on Tuesday when she was approached by a man.

The man struck her on the head with a piece of concrete before pulling out a knife and sexually assaulting her, police said.

Citizens in the area confronted the man, prompting him to flee.

The victim was hospitalized for her injuries.

The suspect is described as six foot tall, in his mid-to-late 20s with a thin build and short black hair.

He was wearing a red short-sleeve shirt, black track pants with white vertical stripes, black and white sneakers and a black backpack.

If you know anything contact police.