York Regional Police released a composite sketch of a man accused of sexually assaulting an 18-year-old woman near the Newmarket GO bus terminal during the early hours of New Year's Day.

The woman told police she was grabbed, forced to the ground, and assaulted by a man who approached her on a pathway parallel to Davis Drive after leaving the terminal around 3 a.m..

The suspect is described as being five-feet-nine inches tall, with a lean build, and about 30 to 50 years of age. 

A man who witnessed the alleged assault says the suspect wore a light-grey jacket, a black-hooded sweater, black neck warmer, and black boots. 

Investigators do not believe this incident is linked to other ongoing sexual assault investigations in the Newmarket area. 

Police are asking anyone with further information to come forward.