Burnaby RCMP have released a sketch of a suspect in a serious sex assault that took place on Burnaby Mountain around 12:40 p.m. PT Thursday.

At a press conference Friday afternoon, police said the attack took place on a small path off the Urban Trail, south of Lougheed Highway.

The place where the assault occurred is accessed by crossing a fence, police said.

The victim was taken to hospital to be treated for her injuries and was allowed home today.

Police have released a sketch depicting a suspect in a serious sex assault that took place in Burnaby on Thursday. (RCMP)

Police would not confirm the age of the victim, nor comment on whether there is any connection to a high school located close by.

An earlier description has now been revised, with the suspect's hair now described as close-cropped and straw coloured.

Police have released a detailed description of the suspect:

Caucasian male with a slim build.

Five feet seven inches in height.

Between 40 and 50 years old.

Wearing black gloves, a grey hoodie, a black jacket, black Adidas runners with green writing, and grey sweat pants with muddy cuffs.

Burnaby RCMP released a detailed map showing the location of a sex assault that took place on Thursday. (Burnaby RCMP)

The suspect fled through the bushes on foot towards Lougheed Mall.

Police continued to caution people to walk in groups or pairs if they are heading out in the area, and to let others know where they are going and when to expect them back.

"We are cautioning everyone that someone is still out there," Staff Sgt. Maj. John Buis said.

"We will continue [to investigate] until we find this person."

Burnaby RCMP are asking anyone who may have seen the man to contact the serious crime section at 604-294-7922, or Crime Stoppers.