4 June 2012 Last updated at 23:26 ET

Epsom Derby sex attacker hunted by police

The attack happened during the Epsom Derby races, which the Queen attended on Saturday afternoon

A teenager who sexually assaulted a 15-year-old girl during the Epsom Derby is being hunted by police.

The victim told police she was attacked in a field close to the Surrey course's music and fairground area, where she met the boy.

Surrey Police said the girl was attacked at about 16:00 BST on Saturday and reported it to officers about two hours later.

The Queen kicked off her Diamond Jubilee celebrations at the course.

Police confirmed they are hunting a boy, aged 16 or 17. They have quizzed some race-goers about the assault.

Det Insp Oana King said it was "obviously a very traumatic experience" for the victim.

Witness sought

"Thankfully this kind of offence is extremely rare and I would like to reassure members of the public that we are doing all we can to identify the perpetrator and bring him to justice," Det Insp King said.

"[We] are keen to speak to anyone who may have seen the suspect prior to or after this offence."

A woman who reported the attack to St John Ambulance staff after overhearing a conversation about it, is being sought by officers.

"I would urge this woman to come forward as she may have vital information which could assist the ongoing investigation," said Det Insp King.

The girl's attacker is described as white, skinny but muscular, with a prominent wide jaw line, short gingery-blond hair and a pale, spotty complexion.

He was wearing a long-sleeved, dark blue top and baggy blue jeans, and was with a boy of a similar age.